Claude Opus 5.5 API: coding, speed, and cost

Claude Opus 5.5 API users on TTAPI now have a new model ID for long coding and knowledge-work tasks: claude-opus-5-5. Anthropic introduced Opus 5.5 on September 22, 2026 and describes better results than Opus 5, clearer communication, faster output, and fewer tokens spent to finish typical work.

The most useful distinction is task efficiency. Anthropic says Opus 5.5 costs about 40% less than Opus 5 on typical workloads, because the token prices fell and the model often needs fewer tokens or tool calls. That is a vendor claim about its evaluated workloads. Measure your own accepted-result cost on TTAPI before assuming the same saving.

Anthropic reports stronger results for Opus 5.5 than Opus 5 on long-running command-line and repository tasks. Its published table lists Terminal-Bench 4.0 at 66.4% versus 52.3% for Opus 5, FrontierCode v1.1 at 54.4% versus 48.0%, and CursorBench 4.0 at 57.8% versus 46.6%. These are not TTAPI-run results, and effort settings differ by benchmark.

In practice, test a codebase-wide change rather than a short code question: give each model the same repository state, failing tests, tools, and acceptance checks. Count passed tests, unrelated edits, tool calls, review corrections, elapsed time, and billable tokens. One completed task says more about your workflow than a broad leaderboard rank.

Opus 5.5 is also positioned for research, financial analysis, business workflows, and document or presentation creation. Anthropic reports a GDPval-AA v2.1 score of 1846 Elo for Opus 5.5, compared with 1708 for Opus 5. Its launch examples emphasize source checking, complete deliverables, and clear writing that makes long sessions easier to review.

For a TTAPI evaluation, give both models the same source bundle and require every important number or quote to be traceable. Score missing facts, unsupported claims, structure, and revision effort. If a model produces a persuasive but unsupported report, it has failed even if the prose reads well.

The current TTAPI catalog lists Opus 5.5 at $4 per million input tokens and $20 per million output tokens, versus $5 and $25 for Opus 5. Cached input is listed at $0.2 versus $0.5 per million. These rates are from the TTAPI price data and should be checked against live billing before production use.

Anthropic says Opus 5.5 produces output more than 30% faster than Opus 5 in its tests. Its direct-platform Fast mode is a separate option; do not assume that mode or its price is exposed by every TTAPI route. Compare latency and total cost per accepted task under the exact TTAPI request configuration your product will use.

Anthropic reports a stronger safeguard stack and better resistance to prompt injection across coding, browsing, tool use, and computer use. Its launch also describes preserved thinking, which can affect applications that edit earlier assistant thinking content. These are provider product behaviors; check the current TTAPI Messages reference before assuming every provider-side setting is available through the gateway.

For coding agents, preserve review gates for file changes and external actions. For financial, legal, or clinical documents, require source checks and human sign-off. Better model scores do not establish that an application can skip its own validation.

TTAPI lists claude-opus-5-5 on the Anthropic-compatible Messages endpoint. The cURL request below sends one focused review task with the TTAPI key in x-api-key. It uses the current TTAPI request profile and leaves provider-specific thinking and Fast mode controls out until their gateway support is confirmed.

Begin with one representative task and save the model ID, response, usage, elapsed time, and acceptance result. Compare the same request against Opus 5 if you are deciding whether to upgrade. Report the result as your own test only after running it; the published scores above remain Anthropic's evidence.

curl --request POST \
  --url 'https://api.ttapi.io/v1/messages' \
  --header "x-api-key: $TTAPI_KEY" \
  --header 'Content-Type: application/json' \
  --data '{
  "model": "claude-opus-5-5",
  "max_tokens": 1024,
  "messages": [
    {
      "role": "user",
      "content": "Review this TypeScript service migration plan. Identify missing checks, then propose a short acceptance checklist."
    }
  ]
}'

• Keep TTAPI_KEY in the server environment.
• Use the exact model ID claude-opus-5-5 on /v1/messages.
• Check the current Messages fields and token billing before shipping.
• Keep the Opus 5 request available as a controlled comparison.