Claude Sonnet 5.5 Release Date: September 28, 2026
Claude Sonnet 5.5 release date and confirmed facts
| Release question | Confirmed position on September 29, 2026 |
|---|---|
| When did Anthropic release it? | September 28, 2026 |
| What is the official model ID? | claude-sonnet-5-5 |
| What does it accept and produce? | Text and image input; text output |
| What are the standard context and output limits? | 1M context; up to 128K output tokens |
| Did standard input/output token prices fall against Sonnet 5? | No; the official rates remain $2 / $10 per million tokens |
| Where should EvoLink users check their route and price? | The existing Sonnet 5.5 model page and account-specific integration information |
What changed for developers?
The release makes Sonnet 5.5 a concrete evaluation candidate. Anthropic describes improvements in everyday coding and tool-based work; these are provider claims, not an EvoLink performance guarantee. A useful evaluation should measure whether your tasks finish with fewer corrections, within the same quality and latency requirements.
Lower task cost is different from a lower token price
The official input/output rates did not change against Sonnet 5. A task may nevertheless cost less if it uses fewer output tokens or needs fewer repair attempts. It can also cost more if you raise effort, extend the conversation, or repeatedly retry a failing workflow.
What to verify before switching a live application
- Confirm the version and route. Use the documented model ID and the intended gateway endpoint. A consumer subscription is not evidence of API access.
- Check request and response compatibility. Review thinking, tools, history, and streaming behavior before comparing output quality.
- Replay representative work. Include routine tasks and recent failures, with the same acceptance criteria as your existing model.
- Inspect the bill and completion time. Count retries and cache behavior; do not judge only by the first response or headline token price.
- Keep rollback available. Preserve the working model, prompts, parsing, tools, and retry settings as one tested configuration.
EvoLink's unified gateway reduces the work of maintaining separate integration entry points. It does not remove the need to test model-specific behavior or automatically configure your application's fallback policy.
Which follow-up decision applies to you?
| Your situation | Next useful action |
|---|---|
| Sonnet 5 already meets your requirements | Run a paired upgrade test before replacing it |
| You need to choose between Sonnet and Opus | Compare task complexity, accepted outcomes, and total cost |
| You are integrating a new application | Review the Sonnet 5.5 product page, route controls, and current prices |
| Your decision depends on a particular tool or beta feature | Confirm support on the intended route before building around it |
Release timeline
- September 22, 2026: the Opus 5.5 announcement named Sonnet 5.5 as a forthcoming release.
- September 28, 2026: Anthropic published the Sonnet 5.5 release announcement.
- September 29, 2026: this article replaced its pre-release guidance with confirmed release facts and links to upgrade and selection guidance.
We retain this URL so earlier links continue to reach the current answer. A historical announcement about a future release should not be read as today's availability status.
FAQ
When was Claude Sonnet 5.5 released?
Anthropic released it on September 28, 2026. The earlier September 22 announcement only gave a future window.
Is Sonnet 5.5 still an unconfirmed model?
No. There is now a dated official announcement and version-specific documentation. Platform and account access should still be checked separately.
Did it launch together with Opus 5.5?
No. Opus 5.5 was announced on September 22; Sonnet 5.5 followed on September 28. Each model has its own documentation and route configuration.
Does the release mean my EvoLink request is ready to use?
Check the model page, current account access, and documented route settings, then validate a request and its billing. An upstream release alone does not verify your application configuration.
Is Sonnet 5.5 cheaper than Sonnet 5?
The official standard input/output token rates are unchanged. Actual cost depends on tokens consumed, caching, retries, effort, and how many results your application accepts.
Can I replace only the model name?
Do not assume that is sufficient. The migration guide includes breaking changes, and your client may depend on tool, thinking, history, or streaming behavior that needs adjustment.
Does this announcement also confirm Haiku 5.5 availability?
No. A Sonnet release is evidence about Sonnet. Verify any other model from its own announcement and documentation.
Should I stop using Sonnet 5 immediately?
No. Preserve a working baseline while evaluating the successor. Switch when the new configuration meets your application's quality, latency, compatibility, and cost requirements.
