CURRENT MODEL COMPARISON / 2026

Claude Haiku 5.5 vs Claude Sonnet 5.5

Does the new Haiku release handle your queue well enough to replace Sonnet for routine requests?

Reviewed Live model evidence ↗
Anthropic

Claude Haiku 5.5↗

An October 2026 Claude release aimed at high-volume, latency-sensitive work, with adaptive thinking.

Access type
Hosted API
Original release date
Model ID
claude-haiku-5-5
Announced context
1 million tokens
Announced maximum output
128,000 tokens
Thinking
Adaptive thinking with effort control
License / terms
Provider service terms

Migration from Haiku 4.5 needs attention: manual budget_tokens thinking, sampling parameters and assistant prefill can return 400 errors on Haiku 5.5.

Official source ↗Latest artifacts and release journal →
Anthropic

Claude Sonnet 5.5↗

The September 2026 Sonnet release, announced across the Claude API and supported cloud platforms.

Access type
Hosted API
Original release date
Model ID
claude-sonnet-5-5
Announced access
Claude API and supported AWS, Google Cloud and Microsoft platforms
Latest lifecycle note
Cache-read price update announced October 7, 2026
License / terms
Provider service terms

Use the exact Claude endpoint and current model documentation for limits and prices. Cache-read pricing changed on October 7, 2026; a launch-era estimate can be stale.

Official source ↗Latest artifacts and release journal →

The decision to test

Start with routine classification and extraction, then add the cases that require escalation. Haiku 5.5 launched October 7, 2026, and Sonnet 5.5 launched September 28. Haiku is positioned for high volume, but your measured error and retry rates decide whether it can handle the workload.

Treat Haiku migration as an API change

Haiku 5.5 uses adaptive thinking with effort control. The official notes warn that manual budget_tokens thinking, temperature, top_p, top_k and assistant prefill can return 400 errors. Fix the request adapter before drawing a latency or quality conclusion.

Design an escalation rule from errors

Label failures by task and difficulty. A routing rule can use schema validation or uncertainty signals, but it should be evaluated on a held-out set. Include both the first attempt and any Sonnet retry in cost and latency.

Three criteria for this comparison

  1. Incorrect fields on labeled extraction cases
  2. Tail latency at the same queue and effort settings
  3. Retries and escalation per accepted result

Run a fair comparison

Use the same representative inputs and a written answer rubric. Pin the model version and record the endpoint, thinking configuration, quantization when known, context length, output allowance and concurrency. Preserve native request differences in an adapter rather than silently dropping fields.

Measure full request time, error rate and reported usage. For tools, validate arguments and score the result after execution. For images, preserve resolution and preprocessing. A valid response format alone does not establish a correct answer.

Compare cost per accepted result

Calculate input cost plus all billed output, including reasoning where the provider counts it. Add retries and discarded answers. Divide the total by the number of results that pass your quality criteria. Keep API usage cost separate from deployment and engineering cost.

Estimate token costs with the API calculator →

Independent benchmark evidence

Open the full live comparison →
Latest recorded measurements aligned by exact artifact, benchmark version, source and methodology. These are source results, not tests of Flonno's deployment.
Benchmark / sourceClaude Haiku 5.5Claude Sonnet 5.5
Artificial Analysis Intelligence Indexv4.3 · Artificial Analysis43.4 index_pointsMeasured Oct 8, 2026Original result ↗56 index_pointsMeasured Sep 29, 2026Original result ↗

Artificial Analysis observations are refreshed by the integrated Radar. Differences in artifact, benchmark version or method prevent a score comparison. Read the evidence methodology →

YOUR WORKLOAD

Compare cost per accepted task.

Enter results from your own evaluation. A task should count once it meets your written quality criteria. Include failed attempts and retries in total spend. These inputs stay in this browser and are not a Flonno benchmark.

Claude Haiku 5.5
Claude Sonnet 5.5
Claude Haiku 5.5

Enter all four values. Attempted tasks must be at least one; accepted tasks cannot exceed attempted tasks.

Claude Sonnet 5.5

Enter all four values. Attempted tasks must be at least one; accepted tasks cannot exceed attempted tasks.

Turn evidence into a deployment decision

A source benchmark can inform your shortlist, while your evaluation shows whether a model finishes the work at an acceptable cost. Keep the chosen endpoint, processing terms and output limits in the decision record. Inclusion in the Radar does not mean the model is served by Flonno.

For the API currently offered here, explore Qwen3.8 Flash 27B and the production evaluation guide.

Release coverage and updates

Model journal →

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