# Claude Fast Mode for Opus 5.5: Cost and When It Pays

> Anthropic took Claude Opus 5.5 fast mode out of research preview on the API on 15 Oct 2026. What it costs and when a team should pay for the speed.

25 October 2026 · Plain English · What's new · 6 min read · https://bridge-terminal.com/atlas/blog/claude-fast-mode-opus-5-5-cost/

## The short version

- Fast mode runs the same Claude Opus 5.5 model with up to 2.5 times more output per second, at a higher price per token ($8 input, $40 output per million tokens).
- On 15 October 2026 Anthropic took fast mode for Opus 5.5 out of research preview on the Claude API, so it needs no beta header or access request there.
- In Claude Code on a Pro, Max, Team or Enterprise plan, fast mode is billed from usage credits, not from the plan's included usage.
- Fast mode pays off when a person waits on the answer, such as live debugging, and rarely for long unattended tasks.
- Atlas has no fast mode today; it is coming to Atlas, built in, with no setup. Atlas's engineers run on your Claude plan's usage meanwhile.

Fast mode is a setting that makes Claude's Opus models write their answers up to 2.5 times faster, in return for a higher price per token. According to Anthropic's release notes, on 15 October 2026 fast mode for Claude Opus 5.5 came out of research preview on the Claude API. If your team uses an AI coding agent, the question is no longer "can we get it?" but "is the speed worth the money for this kind of work?"

This article explains what changed, what fast mode costs, when it is worth paying for, and where Atlas stands on it.

## What is Claude fast mode?

Fast mode is not a smarter or different model. Anthropic's documentation says it runs the same model with a faster setup behind the scenes, and that there is no change to intelligence or capabilities.

What you get is speed in one specific place: output tokens per second, which is how fast the answer is written out. A token is a small chunk of text, roughly a word or part of one. Anthropic says the benefit is in output speed, not in the time to first token, so the first word does not appear sooner. A long answer simply finishes sooner. The figure is "up to" 2.5 times, not a promise for every request.

## What changed on 15 October 2026?

Until then, fast mode on Anthropic's API was a research preview, meaning an unfinished feature that may change. You had to send a special beta header (a label attached to a request that marks it as using an unfinished feature) and ask for access.

The Claude Platform release notes for 15 October 2026 say fast mode is out of research preview for Opus 5.5 and you no longer need to request access. The API documentation adds:

- Opus 5.5 needs no beta header and no access request. Requests that still send the header keep working.
- Opus 5.5 has a default fast mode rate limit on the Start, Build and Scale usage tiers, so most paying API accounts can use it straight away.
- Fast mode on the older Opus 5 and Opus 4.8 stays in research preview and still needs the header.
- The same day, fast mode for Opus 5.5 became available on Claude in Microsoft Foundry for deployments hosted on Azure. A 22 October entry says it is also available on Claude Models on Google Cloud (Anthropic managed).

One detail to watch: when we read it on 25 October, the separate Claude Code documentation page for fast mode still carried a "research preview" note. So the label differs between the API pages and the Claude Code page. The prices below are the same on both.

## How much does fast mode cost?

Anthropic prices fast mode per million tokens (MTok), counted separately for what goes in and what comes out:

| Model | Input | Output |
| - | - | - |
| Claude Opus 5.5 | $8 per MTok | $40 per MTok |
| Claude Opus 5 and Opus 4.8 | $10 per MTok | $50 per MTok |

The price is the same across the whole context window, which is the amount of text the model can hold in mind at once. Other price modifiers, such as the discount for cached text, apply on top.

There is one trap for people who switch it on mid-task. The Claude Code documentation says the first time you enable fast mode in a conversation, you pay the full fast mode price for the entire conversation so far. The deeper into a long session, the more that single switch costs. Turning it on at the start of a session keeps that charge smallest. The charge applies once per conversation, so toggling off and on again does not repeat it.

## How do you turn it on in Claude Code?

In the Claude Code terminal tool, you type `/fast`, press Space to switch it on, and press Enter to confirm. A small ↯ icon next to the prompt shows that fast mode is active. Per the documentation, Opus 5.5 is the default fast mode model from Claude Code version 2.1.280 on. If your current model does not support fast mode, switching it on also moves you to Opus.

The rules that matter to a business owner or manager are about who pays and who may switch it on:

- On Pro, Max, Team and Enterprise plans, fast mode is available through usage credits only. It is not included in the subscription rate limits, and it draws from credits even when you still have plan usage left. On Team and Enterprise, the organization pays from its usage credits.
- Usage credits must be turned on first. Until then, `/fast` reports "Fast mode requires usage credits".
- On Team and Enterprise, fast mode is off by default. An Owner has to enable it for the organization.
- Companies can set "per-session opt-in", so each session starts with fast mode off. Anthropic notes this is useful for controlling costs when people run several sessions at once.
- Fast mode has its own rate limit. When you hit it, Claude Code drops back to standard speed and price, then switches fast mode back on when the cooldown ends.
- Fast mode is not available through Amazon Bedrock, Google Cloud's Agent Platform, Microsoft Foundry or Claude Platform on AWS when used from Claude Code. On the API it does not work with the Batch API or with a Priority Tier commitment.

## When is fast mode worth paying for?

Anthropic's own guidance is the clearest here. Fast mode suits interactive work where waiting hurts:

- Rapid back-and-forth on code changes.
- Live debugging.
- Time-sensitive work against a deadline.

Standard speed suits long autonomous tasks, batch processing, automated pipelines and cost-sensitive work better. If nobody is watching the screen, a faster answer saves nobody's time, and you still pay the higher rate.

A simple test for a team: is a person sitting and waiting? If yes, a few minutes saved may be worth the extra tokens. If the agent is working through a long task overnight or in the background, leave it at standard speed.

Fast mode is also not the only way to get quicker answers. Lowering the effort level makes the model think less, which is faster but may lower quality on complex tasks. Fast mode keeps the quality and trades money for speed. Anthropic says you can combine the two for maximum speed on straightforward tasks.

## What should a team do this week?

1. Decide who may use it. On Team or Enterprise, nothing happens until an Owner switches it on, so this is a deliberate choice.
2. Set a budget line for usage credits, since fast mode spends them directly.
3. Ask engineers to turn it on at the start of a session, not halfway through a long one.
4. Keep it for work where a person waits, and review the credit spend after a week.

## Does Atlas use fast mode?

Not today. [Atlas](https://bridge-terminal.com/atlas/) is a software team made of AI engineers, built on Claude Code. Each engineer is its own Claude Code session with a written role, and its model and effort are tuned to that role. Atlas runs on your own Claude plan (Pro or Max), so usage counts against the plan, and it does not offer a fast mode switch.

Fast mode is coming to Atlas, built in, so it will need no setup on your side. Until then, if you want fast mode for your own hands-on work, you can use `/fast` in Claude Code directly with usage credits turned on. Keep in mind that this spends credits outside the plan's included usage. Atlas also offers an optional daily budget that warns at 50% and 80% and pauses at 100%.

## Conclusion

Fast mode is a straight trade: the same Opus 5.5 quality, up to 2.5 times quicker output, at $8 per million input tokens and $40 per million output tokens, billed from usage credits on subscription plans. The 15 October change mainly removes friction for API users. For teams, the real work is deciding when speed is worth the bill, and that usually means only when a person is waiting.

## Questions people ask

### What is fast mode in Claude?

Fast mode runs the same Claude Opus model with a faster setup, giving up to 2.5 times more output tokens per second. It costs more per token and does not change the model's intelligence or capabilities.

### How much does Claude Opus 5.5 fast mode cost?

Anthropic lists fast mode for Opus 5.5 at $8 per million input tokens and $40 per million output tokens. On Claude Code subscription plans it is billed from usage credits, not from the plan's included usage.

### Is fast mode out of research preview?

For Claude Opus 5.5 on the Claude API, yes: Anthropic's release notes of 15 October 2026 say so, and no beta header or access request is needed. Opus 5 and Opus 4.8 remain in research preview, and the Claude Code docs page still showed a research preview note on 25 October.

### When should a team use fast mode?

Use it when a person is waiting on the answer, such as live debugging or quick iteration. Anthropic suggests standard speed for long autonomous tasks, batch processing and cost-sensitive work.

### Does Atlas support fast mode?

Not yet. Atlas runs its engineers on your own Claude plan, with model and effort tuned per role. Fast mode is coming to Atlas, built in, so it will need no setup.

## About Atlas: Fast mode and the Atlas team's plan usage

Atlas engineers are Claude Code sessions that run on your own Claude plan, with model and effort tuned per role. Atlas has no fast mode switch today; it is coming to Atlas, built in, so it will need no setup. Until then, Atlas's optional daily budget warns at 50% and 80% and pauses the team at 100%. — https://bridge-terminal.com/atlas/

## Sources

- [Fast mode - Claude API docs](https://platform.claude.com/docs/en/build-with-claude/fast-mode)
- [Speed up responses with fast mode - Claude Code docs](https://code.claude.com/docs/en/fast-mode)
- [Claude Platform release notes, October 2026](https://platform.claude.com/docs/en/release-notes/overview)

_Researched and drafted with Claude, then checked against the sources above. Atlas is an independent product, not affiliated with Anthropic or OpenAI._