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Neural encoding enables more-efficient recovery of lost audio packets

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Packet loss is a big problem for real-time voice communication over the Internet. Everyone has been in the situation where the network is becoming unreliable and enough packets are getting lost that it’s hard — or impossible — to make out what the other person is saying.

One way to fight packet loss is through redundancy, in which each new packet includes information about prior packets. But existing redundancy schemes either have limited scope — carrying information only about the immediately preceding packet, for instance — or scale inefficiently.

The Deep REDundancy (DRED) technology from the Amazon Chime SDK team significantly improves quality and intelligibility under packet loss by efficiently transmitting large amounts of redundant information. Our approach leverages the ability of neural vocoders to reconstruct informationally rich speech signals from informationally sparse frequency spectrum snapshots, and we use a neural encoder to compress those snapshots still further. With this approach, we are able to load a single packet with information about as many as 50 prior packets (one second of speech) with minimal increase in bandwidth.

We describe our approach in a paper that we will present at this year’s ICASSP.

Redundant audio

All modern codecs (coder/decoders) have so-called packet-loss-concealment (PLC) algorithms that attempt to guess the content of lost packets. Those algorithms work fine for infrequent, short losses, as they can extrapolate phonemes to fill in gaps of a few tens of milliseconds. However, they cannot (and certainly should not try to) predict the next phoneme or word from the conversation. To deal with significantly degraded networks, we need more than just PLC.

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One option is the 25-year-old spec for REDundant audio data (often referred to as just RED). Despite its age, RED is still in use today and is one of the few ways of transmitting redundant data for WebRTC, a popular open-source framework for real-time communication over the Web. RED has the advantage of being flexible and simple to use, but it is not very efficient. Transmitting two copies of the audio requires … twice the bitrate.

The Opus audio codec — which is the default codec for WebRTC — introduced a more efficient scheme for redundancy called low-bit-rate redundancy (LBRR). With LBRR, each new audio packet can include a copy of the previous packet, encoded at a lower bit rate. That has the advantage of lowering the bit rate overhead. Also, because the scheme is deeply integrated into Opus, it can be simpler to use than RED.

That being said, the Opus LBRR is limited to just one frame of redundancy, so it cannot do much in the case of a long burst of lost packets. RED does not have that limitation, but transmitting a large number of copies would be impractical due to the overhead. There is always the risk that the extra redundancy will end up causing congestion and more losses.

With every new voice packet (blue), Opus’s low-bit-rate-redundancy (LBRR) mechanism includes a compressed copy of the previous packet (green). When three consecutive packets are lost (red x’s), two of them are unrecoverable, and a packet-loss-concealment (PLC) algorithm must fill in the gaps.

Deep REDundancy (DRED)

In the past few years, we have seen neural speech codecs that can produce good quality speech at only a fraction of the bit rate required by traditional speech codecs — typically less than three kilobits per second (3 kb/s). That was unthinkable just a few years ago. But for most real-time-communication applications, neural codecs aren’t that useful, because just the packet headers required by the IP/UDP/RTP protocols take up 16 kb/s.

However, for the purpose of transmitting a large amount of redundancy, a neural speech codec can be very useful, and we propose a Deep REDundancy codec that has been specifically designed for that purpose. It has a different set of constraints than a regular speech codec:

  • The redundancy in different packets needs to be independent (that’s why we call it redundancy in the first place). However, within each packet, we can use as much prediction and other redundancy elimination as we like since IP packets are all-or-nothing (no corrupted packets).
  • We want to encode meaningful acoustic features rather than abstract (latent) ones to avoid having to standardize more than needed and to leave room for future technology improvements.
  • There is a large degree of overlap between consecutive redundancy packets. The encoder should leverage this overlap and should not need to encode each redundancy packet from scratch. The encoding complexity should remain constant even as we increase the amount of redundancy.
  • Since short bursts are more common than long ones, the redundancy decoder should be able to decode the most recent audio quickly but may take longer to decode older signals.
  • The Opus decoder has to be able to switch between decoding DRED, PLC, LBRR, and regular packets at any time.

Neural vocoders

Let’s take a brief detour and discuss neural vocoders. A vocoder is an algorithm that takes in acoustic features that describe the spectrum of a speech signal over a short span of time and generates the corresponding (continuous) speech signal. Vocoders can be used in text-to-speech, where acoustic features are generated from text, and for speech compression, where the encoder transmits acoustic features, and a vocoder generates speech from the features.

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Vocoders have been around since the ’70s, but none had ever achieved acceptable speech quality — until neural vocoders like WaveNet came about and changed everything. WaveNet itself was all but impossible to implement in real time (even on a GPU), but it led to lower-complexity neural vocoders, like the LPCNet vocoder we’re using here.

Like many (but not all) neural vocoders, LPCNet is autoregressive, in that it produces the audio samples that best fit the previous samples — whether the previous samples are real speech or speech synthesized by LPCNet itself. As we will see below, that property can be very useful.

DRED architecture

The vocoder’s inputs — the acoustic features — don’t describe the full speech waveform, but they do describe how the speech sounds to the human ear. That makes them lightweight and predictable and thus ideal for transmitting large amounts of redundancy.

The idea behind DRED is to compress the features as much as possible while ensuring that the recovered speech is still intelligible. When multiple packets go missing, we wait for the first packet to arrive and decode the features it contains. We then send those features to a vocoder — in our case, LPCNet — which re-synthesizes the missing speech for us from the point where the loss occurred. Once the “hole” is filled, we resume with Opus decoding as usual.

Combining the constraints listed earlier leads to the encoder architecture depicted below, which enables efficient encoding of highly redundant acoustic features — so that extended holes can be filled at the decoder.

Every 20 milliseconds, the DRED encoder encodes the last 40 milliseconds of speech. The decoder works backward, as the most recently transmitted audio is usually the most important.

The DRED encoder works as follows. Every 20 milliseconds (ms), it produces a new vector that contains information about the last 40 ms of speech. Given this overlap, we need only half of the vectors to reconstruct the complete speech. To avoid our redundancy’s being itself redundant, in a given 20 ms packet, we include only every other redundancy coding vector, so the redundancy encoded in a given packet covers nonoverlapping segments of the past speech. In terms of the figure above, the signal can be recovered from just the odd/purple blocks or just the even/blue blocks.

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The degree of redundancy is determined by the number of past chunks included in each packet; each chunk included in the redundancy coding corresponds to 40 ms of speech that can be recovered. Furthermore, rather than representing each chunk independently, the encoder takes advantage of the correlation between successive chunks and extracts a sort of interchunk difference to encode.

For decoding, to be able to synthesize the whole sequence, all we need is a starting point. But rather than decoding forward in time, as would be intuitive, we choose an initial state that corresponds to the most recent chunk; from there, we decode going backward in time. That means we can get quickly to the most recent audio, which is more likely to be useful. It also means that we can transmit as much — or as little — redundancy as we want just by choosing how many chunks to include in a packet.

Rate-distortion-optimized variational autoencoder

Now let’s get into the details of how we minimize the bit rate to code our redundancy. Here we turn to a widely used method in the video coding world, rate distortion optimization (RDO), which means trying to simultaneously reduce the bit rate and the distortion we cause to the speech. In a regular autoencoder, we train an encoder to find a simple — typically, low-dimensional — vector representation of an input that can then be decoded back to something close to the original.

In our rate-distortion-optimized variational autoencoder (RDO-VAE), instead of imposing a limit on the dimensionality of the representation, we directly limit the number of bits required to code that representation. We can estimate the actual rate (in bits) required to code the latent representation, assuming entropy coding of a quantized Laplace distribution. As a result, not only do we automatically optimize the feature representation, but the training process automatically discards any useless dimensions by setting them to zero. We don’t need to manually choose the number of dimensions.

Moreover, by varying the rate-distortion trade-off, we can train a rate-controllable quantizer. That allows us to use better quality for the most recent speech (which is more likely to be used) and a lower quality for older speech that would be used only for a long burst of loss. In the end, we use an average bit rate of around 500 bits/second (0.5 kb/s) and still have enough information to reconstruct intelligible speech.

Once we include DRED, this is what the packet loss scenario described above would look like:

With LBRR, each new packet (blue) includes a compressed copy of the previous packet (green); with DRED, it includes highly compressed versions of up to 50 prior packets (red). In this case, DRED’s redundancy is set at 140 ms (seven packets).

Although it is illustrated for just 70 milliseconds of redundancy, we scale this up to one full second of redundancy contained in each 20-millisecond packet. That’s 50 copies of the information being sent, on the assumption that at least one will make it to its destination and enable reconstruction of the original speech.

Revisiting packet loss concealment

So what happens when we lose a packet and don’t have any DRED data for it? We still need to play out something — and ideally not zeros. In that case, we can just guess. Over a short period of time, we can still predict acoustic features reasonably well and then ask LPCNet to fill in the missing audio based on those features. That is essentially what PLC does, and doing it with a neural vocoder like LPCNet works better than using traditional PLC algorithms like the one that’s currently integrated into Opus. In fact, our neural PLC algorithm recently placed second in the Interspeech 2022 Audio Deep Packet Loss Concealment Challenge.

Results

How much does DRED improve speech quality and intelligibility under lossy network conditions? Let’s start with a clip compressed with Opus wideband at 24 kb/s, plus 16 kb/s of LBRR redundancy (40 kb/s total). This is what we get without loss:

To show what happens in lossy conditions, let’s use a particularly difficult — but real — loss sequence taken from the PLC Challenge. If we use the standard Opus redundancy (LBRR) and PLC, the resulting audio is missing large chunks that just cannot be filled:

Lossy audio with LBRR and PLC

If we add our DRED coding with one full second of redundancy included in each packet, at a cost of about 32 kb/s, the missing speech can be entirely recovered:

Overall results of DRED’s evaluation on the full dataset for the original PLC Challenge, using mean opinion score (MOS).

The example above is based on just one speech sequence, but we evaluated DRED on the full dataset for the original PLC Challenge, using mean opinion score (MOS) to aggregate the judgments of human reviewers. The results show that DRED alone (no LBRR) can reduce the impact of packet loss by about half even compared to our previous neural PLC. Also interesting is the fact that LBRR still provides a benefit even when DRED is used. With both LBRR and DRED, the impact of packet loss becomes very small, with just a 0.1 MOS degradation compared to the original, uncompressed speech.

This work is only one example of how Amazon is contributing to improving Opus. Our open-source neural PLC and DRED implementations are available on this development branch, and we welcome feedback and outside collaboration. We are also engaging with the IETF with the goal of updating the Opus standard in a fully compatible way. Our two Internet drafts (draft 1 | draft 2) offer more details on what we are proposing.





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An inside look at Meta’s transition from C to Rust on mobile

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Have you ever worked is legacy code? Are you curious what it takes to modernize systems at a massive scale?

Pascal Hartig is joined on the latest Meta Tech Podcast by Elaine and Buping, two software engineers working on a bold project to rewrite the decades-old C code in one of Meta’s core messaging libraries in Rust. It’s an ambitious effort that will transform a central messaging library that is shared across Messenger, Facebook, Instagram, and Meta’s AR/VR platforms.

They discuss taking on a project of this scope – even without a background in Rust, how they’re approaching it, and what it means to optimize for ‘developer happiness.’

Download or listen to the episode below:

You can also find the episode wherever you get your podcasts, including:

The Meta Tech Podcast is a podcast, brought to you by Meta, where we highlight the work Meta’s engineers are doing at every level – from low-level frameworks to end-user features.

Send us feedback on InstagramThreads, or X.

And if you’re interested in learning more about career opportunities at Meta visit the Meta Careers page.





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Amazon Research Awards recipients announced

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Amazon Research Awards (ARA) provides unrestricted funds and AWS Promotional Credits to academic researchers investigating various research topics in multiple disciplines. This cycle, ARA received many excellent research proposals from across the world and today is publicly announcing 73 award recipients who represent 46 universities in 10 countries.

This announcement includes awards funded under five call for proposals during the fall 2024 cycle: AI for Information Security, Automated Reasoning, AWS AI, AWS Cryptography, and Sustainability. Proposals were reviewed for the quality of their scientific content and their potential to impact both the research community and society. Additionally, Amazon encourages the publication of research results, presentations of research at Amazon offices worldwide, and the release of related code under open-source licenses.

Recipients have access to more than 700 Amazon public datasets and can utilize AWS AI/ML services and tools through their AWS Promotional Credits. Recipients also are assigned an Amazon research contact who offers consultation and advice, along with opportunities to participate in Amazon events and training sessions.

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“Automated Reasoning is an important area of research for Amazon, with potential applications across various features and applications to help improve security, reliability, and performance for our customers. Through the ARA program, we collaborate with leading academic researchers to explore challenges in this field,” said Robert Jones, senior principal scientist with the Cloud Automated Reasoning Group. “We were again impressed by the exceptional response to our Automated Reasoning call for proposals this year, receiving numerous high-quality submissions. Congratulations to the recipients! We’re excited to support their work and partner with them as they develop new science and technology in this important area.”

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“At Amazon, we believe that solving the world’s toughest sustainability challenges benefits from both breakthrough scientific research and open and bold collaboration. Through programs like the Amazon Research Awards program, we aim to support academic research that could contribute to our understanding of these complex issues,” said Kommy Weldemariam, Director of Science and Innovation Sustainability. “The selected proposals represent innovative projects that we hope will help advance knowledge in this field, potentially benefiting customers, communities, and the environment.”

ARA funds proposals throughout the year in a variety of research areas. Applicants are encouraged to visit the ARA call for proposals page for more information or send an email to be notified of future open calls.

The tables below list, in alphabetical order by last name, fall 2024 cycle call-for-proposal recipients, sorted by research area.

AI for Information Security

Recipient University Research title
Christopher Amato Northeastern University Multi-Agent Reinforcement Learning Cyber Defense for Securing Cloud Computing Platforms
Bernd Bischl Ludwig Maximilian University of Munich Improving Generative and Foundation Models Reliability via Uncertainty-awareness
Shiqing Ma University Of Massachusetts Amherst LLM and Domain Adaptation for Attack Detection
Alina Oprea Northeastern University Multi-Agent Reinforcement Learning Cyber Defense for Securing Cloud Computing Platforms
Roberto Perdisci University of Georgia ContextADBench: A Comprehensive Benchmark Suite for Contextual Anomaly Detection

Automated Reasoning

Recipient University Research title
Nada Amin Harvard University LLM-Augmented Semi-Automated Proofs for Interactive Verification
Suguman Bansal Georgia Institute of Technology Certified Inductive Generalization in Reinforcement Learning
Ioana Boureanu University of Surrey Phoebe+: An Automated-Reasoning Tool for Provable Privacy in Cryptographic Systems
Omar Haider Chowdhury Stony Brook University Restricter: An Automatic Tool for Authoring Amazon Cedar Access Control Policies with the Principle of Least Privilege
Stefan Ciobaca Alexandru Ioan Cuza University An Interactive Proof Mode for Dafny
João Ferreira INESC-ID Polyglot Automated Program Repair for Infrastructure as Code
Sicun Gao University Of California, San Diego Monte Carlo Trees with Conflict Models for Proof Search
Mirco Giacobbe University of Birmingham Neural Software Verification
Tobias Grosser University of Cambridge Synthesis-based Symbolic BitVector Simplification for Lean
Ronghui Gu Columbia University Scaling Formal Verification of Security Properties for Unmodified System Software
Alexey Ignatiev Monash University Huub: Next-Gen Lazy Clause Generation
Kenneth McMillan University of Texas At Austin Synthesis of Auxiliary Variables and Invariants for Distributed Protocol Verification
Alexandra Mendes University of Porto Overcoming Barriers to the Adoption of Verification-Aware Languages
Jason Nieh Columbia University Scaling Formal Verification of Security Properties for Unmodified System Software
Rohan Padhye Carnegie Mellon University Automated Synthesis and Evaluation of Property-Based Tests
Nadia Polikarpova University Of California, San Diego Discovering and Proving Critical System Properties with LLMs
Fortunat Rajaona University of Surrey Phoebe+: An Automated-Reasoning Tool for Provable Privacy in Cryptographic Systems
Subhajit Roy Indian Institute of Technology Kanpur Theorem Proving Modulo LLM
Gagandeep Singh University of Illinois At Urbana–Champaign Trustworthy LLM Systems using Formal Contracts
Scott Stoller Stony Brook University Restricter: An Automatic Tool for Authoring Amazon Cedar Access Control Policies with the Principle of Least Privilege
Peter Stuckey Monash University Huub: Next-Gen Lazy Clause Generation
Yulei Sui University of New South Wales Path-Sensitive Typestate Analysis through Sparse Abstract Execution
Nikos Vasilakis Brown University Semantics-Driven Static Analysis for the Unix/Linux Shell
Ping Wang Stevens Institute of Technology Leveraging Large Language Models for Reasoning Augmented Searching on Domain-specific NoSQL Database
John Wawrzynek University of California, Berkeley GPU-Accelerated High-Throughput SAT Sampling

AWS AI

Recipient University Research title
Panagiotis Adamopoulos Emory University Generative AI solutions for The Spillover Effect of Fraudulent Reviews on Product Recommendations
Vikram Adve University of Illinois at Urbana–Champaign Fellini: Differentiable ML Compiler for Full-Graph Optimization for LLM Models
Frances Arnold California Institute of Technology Closed-loop Generative Machine Learning for De Novo Enzyme Discovery and Optimization
Yonatan Bisk Carnegie Mellon University Useful, Safe, and Robust Multiturn Interactions with LLMs
Shiyu Chang University of California, Santa Barbara Cut the Crap: Advancing the Efficient Communication of Multi-Agent Systems via Spatial-Temporal Topology Design and KV Cache Sharing
Yuxin Chen University of Pennsylvania Provable Acceleration of Diffusion Models for Modern Generative AI
Tianlong Chen University of North Carolina at Chapel Hill Cut the Crap: Advancing the Efficient Communication of Multi-Agent Systems via Spatial-Temporal Topology Design and KV Cache Sharing
Mingyu Ding University of North Carolina at Chapel Hill Aligning Long Videos and Language as Long-Horizon World Models
Nikhil Garg Cornell University Market Design for Responsible Multi-agent LLMs
Jessica Hullman Northwestern University Human-Aligned Uncertainty Quantification in High Dimensions
Christopher Jermaine Rice University Fast, Trusted AI Using the EINSUMMABLE Compiler
Yunzhu Li Columbia University Physics-Informed Foundation Models Through Embodied Interactions
Pattie Maes Massachusetts Institute of Technology Understanding How LLM Agents Deviate from Human Choices
Sasa Misailovic University of Illinois at Urbana–Champaign Fellini: Differentiable ML Compiler for Full-Graph Optimization for LLM Models
Kristina Monakhova Cornell University Trustworthy extreme imaging for science using interpretable uncertainty quantification
Todd Mowry Carnegie Mellon University Efficient LLM Serving on Trainium via Kernel Generation
Min-hwan Oh Seoul National University Mutually Beneficial Interplay Between Selection Fairness and Context Diversity in Contextual Bandits
Patrick Rebeschini University of Oxford Optimal Regularization for LLM Alignment
Jose Renau University of California, Santa Cruz Verification Constrained Hardware Optimization using Intelligent Design Agentic Programming
Vilma Todri Emory University Generative AI solutions for The Spillover Effect of Fraudulent Reviews on Product Recommendations
Aravindan Vijayaraghavan Northwestern University Human-Aligned Uncertainty Quantification in High Dimensions
Wei Yang University of Texas at Dallas Optimizing RISC-V Compilers with RISC-LLM and Syntax Parsing
Huaxiu Yao University of North Carolina at Chapel Hill Aligning Long Videos and Language as Long-Horizon World Models
Amy Zhang University of Washington Tools for Governing AI Agent Autonomy
Ruqi Zhang Purdue University Efficient Test-time Alignment for Large Language Models and Large Multimodal Models
Zheng Zhang Rutgers University-New Brunswick AlphaQC: An AI-powered Quantum Circuit Optimizer and Denoiser

AWS Cryptography

Recipient University Research title
Alexandra Boldyreva Georgia Institute of Technology Quantifying Information Leakage in Searchable Encryption Protocols
Maria Eichlseder Graz University of Technology, Austria SALAD – Systematic Analysis of Lightweight Ascon-based Designs
Venkatesan Guruswami University of California, Berkeley Obfuscation, Proof Systems, and Secure Computation: A Research Program on Cryptography at the Simons Institute for the Theory of Computing
Joseph Jaeger Georgia Institute of Technology Analyzing Chat Encryption for Group Messaging
Aayush Jain Carnegie Mellon Large Scale Multiparty Silent Preprocessing for MPC from LPN
Huijia Lin University of Washington Large Scale Multiparty Silent Preprocessing for MPC from LPN
Hamed Nemati KTH Royal Institute of Technology Trustworthy Automatic Verification of Side-Channel Countermeasures for Binary Cryptographic Programs using the HoIBA libary
Karl Palmskog KTH Royal Institute of Technology Trustworthy Automatic Verification of Side-Channel Countermeasures for Binary Cryptographic Programs using the HoIBA libary
Chris Peikert University of Michigan, Ann Arbor Practical Third-Generation FHE and Bootstrapping
Dimitrios Skarlatos Carnegie Mellon University Scale-Out FHE LLMs on GPUs
Vinod Vaikuntanathan Massachusetts Institute of Technology Can Quantum Computers (Really) Factor?
Daniel Wichs Northeastern University Obfuscation, Proof Systems, and Secure Computation: A Research Program on Cryptography at the Simons Institute for the Theory of Computing
David Wu University Of Texas At Austin Fast Private Information Retrieval and More using Homomorphic Encryption

Sustainability

Recipient University Research title
Meeyoung Cha Max Planck Institute Forest-Blossom (Flossom): A New Framework for Sustaining Forest Biodiversity Through Outcome-Driven Remote Sensing Monitoring
Jingrui He University of Illinois at Urbana–Champaign Foundation Model Enabled Earth’s Ecosystem Monitoring
Pedro Lopes University of Chicago AI-powered Tools that Enable Engineers to Make & Re-make Sustainable Hardware
Cheng Yaw Low Max Planck Institute Forest-Blossom (Flossom): A New Framework for Sustaining Forest Biodiversity Through Outcome-Driven Remote Sensing Monitoring





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Independent evaluations demonstrate Nova Premier’s safety

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AI safety is a priority at Amazon. Our investment in safe, transparent, and responsible AI (RAI) includes collaboration with the global community and policymakers. We are members of and collaborate with organizations such as the Frontier Model Forum, the Partnership on AI, and other forums organized by government agencies such as the National Institute of Standards and Technology (NIST). Consistent with Amazon’s endorsement of the Korea Frontier AI Safety Commitments, we published our Frontier Model Safety Framework earlier this year.

Amazon Nova Premier’s guardrails help prevent generation of unsafe content.

During the development of the Nova Premier model, we conducted a comprehensive evaluation to assess its performance and safety. This included testing on both internal and public benchmarks and internal/automated and third-party red-teaming exercises. Once the final model was ready, we prioritized obtaining unbiased, third-party evaluations of the model’s robustness against RAI controls. In this post, we outline the key findings from these evaluations, demonstrating the strength of our testing approach and Amazon Premier’s standing as a safe model. Specifically, we cover our evaluations with two third-party evaluators: PRISM AI and ActiveFence.

Evaluation of Nova Premier against PRISM AI

PRISM Eval’s Behavior Elicitation Tool (BET) dynamically and systematically stress-tests AI models’ safety guardrails. The methodology focuses on measuring how many adversarial attempts (steps) it takes to get a model to generate harmful content across several key risk dimensions. The central metric is “steps to elicit” — the number of increasingly sophisticated prompting attempts required before a model generates an inappropriate response. A higher number of steps indicates stronger safety measures, as the model is more resistant to manipulation. The PRISM risk dimensions (inspired by the MLCommons AI Safety Benchmarks) include CBRNE weapons, violent crimes, non-violent crimes, defamation, and hate, amongst several others.

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Using the BET Eval tool and its V1.0 metric, which is tailored toward non-reasoning models, we compared the recently released Nova models (Pro and Premier) to the latest models in the same class: Claude (3.5 v2 and 3.7 non-reasoning) and Llama4 Maverick, all available through Amazon Bedrock. PRISM BET conducts black-box evaluations (where model developers don’t have access to the test prompts) of models integrated with their API. The evaluation conducted with BET Eval MAX, PRISM’s most comprehensive/aggressive testing suite, revealed significant variations in safety against malicious instructions. Nova models demonstrated superior overall safety performance, with an average of 43 steps for Premier and 52 steps for Pro, compared to 37.7 for Claude 3.5 v2 and fewer than 12 steps for other models in the comparison set (namely, 9.9 for Claude3.7, 11.5 for Claude 3.7 thinking, and 6.5 for Maverick). This higher step count suggests that on average, Nova’s safety guardrails are more sophisticated and harder to circumvent through adversarial prompting. The figure below presents the number of steps per harm category evaluated through BET Eval MAX.

Results of tests using PRISM’s BET Eval MAX testing suite.

The PRISM evaluation provides valuable insights into the relative safety of different Amazon Bedrock models. Nova’s strong performance, particularly in hate speech and defamation resistance, represents meaningful progress in AI safety. However, the results also highlight the ongoing challenge of building truly robust safety measures into AI systems. As the field continues to evolve, frameworks like BET will play an increasingly important role in benchmarking and improving AI safety. As a part of this collaboration Nicolas Miailhe, CEO of PRISM Eval, said, “It’s incredibly rewarding for us to see Nova outperforming strong baselines using the BET Eval MAX; our aim is to build a long-term partnership toward safer-by-design models and to make BET available to various model providers.” Organizations deploying AI systems should carefully consider these safety metrics when selecting models for their applications.

Manual red teaming with ActiveFence

The AI safety & security company ActiveFence benchmarked Nova Premier on Bedrock on prompts distributed across Amazon’s eight core RAI categories. ActiveFence also evaluated Claude 3.7 (non-reasoning mode) and GPT 4.1 API on the same set. The flag rate on Nova Premier was lower than that on the other two models, indicating that Nova Premier is the safest of the three.

Model 3P Flag Rate [↓ is better]
Nova Premier 12.0%
Sonnet 3.7 (non-reasoning) 20.6%
GPT4.1 API 22.4%

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“Our role is to think like an adversary but act in service of safety,” said Guy Paltieli from ActiveFence. “By conducting a blind stress test of Nova Premier under realistic threat scenarios, we helped evaluate its security posture in support of Amazon’s broader responsible-AI goals, ensuring the model could be deployed with greater confidence.”

These evaluations conducted with PRISM and ActiveFence give us confidence in the strength of our guardrails and our ability to protect our customers’ safety when they use our models. While these evaluations demonstrate strong safety performance, we recognize that AI safety is an ongoing challenge requiring continuous improvement. These assessments represent a point-in-time snapshot, and we remain committed to regular testing and enhancement of our safety measures. No AI system can guarantee perfect safety in all scenarios, which is why we maintain monitoring and response systems after deployment.

Acknowledgments: Vincent Ponzo, Elyssa Vincent





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