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Bloom

FreeAPISelf-HostedAgentic

Summary

Bloom generates targeted evaluation suites for arbitrary behavioral traits.

Pricing Plans

Free
Free Tier
No limits; fully open-source

Open Source

Free

Freely available open-source framework

  • Full agentic evaluation pipeline
  • Four-stage system (Understanding, Ideation, Rollout, Judgment)
  • Weights & Biases integration
  • Inspect transcript export
  • Interactive transcript viewer

View full pricing on anthropic.com →

Pricing may have changed since last verified. Check the official site for current plans.

Community Performance Report Card

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Best For: Regression testing, release gating, and tracking mitigations over time, AI safety and alignment research teams, Studying narrow but critical risks that may be missed by broader evaluations, Evaluating frontier AI models for specific behavioral traits, Automating evaluation suite generation without manual engineering

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Pros

  • Reproducible and targeted evaluations that quantify frequency and severity across automatically generated scenarios
  • Evaluations correlate strongly with hand-labelled judgments and reliably separate baseline models from intentionally misaligned ones
  • Researchers can extensively configure Bloom's behavior, through choosing models for each stage, adjusting interactions' length and modality
  • Using Bloom evaluations took only a few days to conceptualize, refine and generate
  • Integrates with Weights & Biases for experiments at scale and exports Inspect-compatible transcripts

Cons

  • Bloom is only as robust as the seeds and judging logic that power it; teams should treat seeds as living governance artifacts, and for ambiguous or highly contextual behaviors, periodic manual review is still necessary
  • Bloom's evaluation suite is unlikely to match the precise distribution of scenarios found in existing benchmarks, and since model behavior can be sensitive to context and prompt variations, direct comparisons are unreliable

Community Reviews

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About

Platforms
Python; integrates with Anthropic and OpenAI models via LiteLLM; supports Weights & Biases
Languages
Python
API Available
Yes
Self-Hosted
Yes
Last Updated
2026-04-20T21:16:31.339Z

Best For

Who it's for

  • Regression testing, release gating, and tracking mitigations over time
  • AI safety and alignment research teams
  • Studying narrow but critical risks that may be missed by broader evaluations
  • Evaluating frontier AI models for specific behavioral traits
  • Automating evaluation suite generation without manual engineering

What it does well

  • Measuring behaviors like delusional sycophancy, long-horizon sabotage, self-preservation and self-preferential bias
  • Regression testing, release gating, and tracking mitigations over time
  • Investigating jailbreak susceptibility, self-preferential bias, and long-horizon sabotage risks
  • Quantifying frequency and severity of target behaviors across generated scenarios
  • Baseline model comparison and intentional misalignment detection

Integrations

Weights & Biases for experiments at scale; Inspect-compatible transcripts; LiteLLM backend for model API calls supporting Anthropic and OpenAI models

Discussion Community

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Frequently Asked Questions

Is Bloom free?
Yes — Bloom is fully free to use. There is no paid tier.
Is Bloom open source?
No — Bloom is a closed-source tool. Source code is not publicly available.
Does Bloom have an API?
Yes. Bloom exposes a developer API. See the official documentation at https://anthropic.com for details.
Can I self-host Bloom?
Yes. Bloom supports self-hosting on your own infrastructure.
When was Bloom released?
Bloom was first released in 2025.
What platforms does Bloom support?
Bloom is available on: Python; integrates with Anthropic and OpenAI models via LiteLLM; supports Weights & Biases.

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