---
id: "2026-05-28-claude-opus-4-8"
url: "https://postcutoff.com/e/2026-05-28-claude-opus-4-8/"
as_of: "2026-11-13T13:49:00+01:00"
date: "2026-05-28"
date_precision: day
category: model-release
importance: 3
confidence: high
status: [Confirmed]
sources: 7
editor: human editor
human_review: null
version: "2026-10-11"
---

As of: 2026-11-13 13:49 CET.
Researched and written by AI agents (Claude Opus 5.5 in Claude Code), with a human editor. How we work: https://postcutoff.com/about/
Canonical page: https://postcutoff.com/e/2026-05-28-claude-opus-4-8/

# Anthropic releases Claude Opus 4.8 with cheaper fast mode and Claude Code "dynamic workflows"

Claude Opus 4.8 (`claude-opus-4-8`) launched on May 28, 2026 at the same $5/$25 price as Opus 4.7. It improved agentic coding, computer use and honesty, and Anthropic said Mythos-class models would reach all customers within weeks. Fast mode (2.5x speed) became three times cheaper, and Claude Code gained 'dynamic workflows' that can fan out to hundreds of parallel subagents.

## Key facts
- Released May 28, 2026; model id claude-opus-4-8; $5/$25 per 1M tokens; fast mode $10/$50
- Context 1M tokens on Claude API, Bedrock and Vertex AI (200K on Microsoft Foundry); 128K output
- Online-Mind2Web 84%; OSWorld-Verified 82.3% (Anthropic)
- Claude Code dynamic workflows (research preview) spawn hundreds of parallel subagents; effort slider added to claude.ai and Cowork
- 'Ultracode' (Claude Code v2.1.154, May 28, per Pilot Shell): a toggle on the /effort slider that makes Claude orchestrate dynamic workflows for substantive tasks; Anthropic's docs call it 'a Claude Code setting rather than a model effort level'. `--effort ultracode` (or Agent SDK effortLevel 'ultracode') turns it on and sets effort to xhigh; the model effort ladder stays low/medium/high/xhigh/max. Uses many more tokens per request. Later popular in 'Opus 5.5 ultracode' demo videos
- Opus 4.8 later served as fallback model for Fable 5 / Opus 5.5 cyber classifier blocks

## What happened

Testers found Opus 4.8 "more reliable and sharper in its judgement" on agentic tasks and more likely to flag uncertainty instead of making unsupported claims. The same day Anthropic announced its $65B Series H. The accompanying Claude Code video promoted `/goal` and `/remote-control` for long-running work.

## Why it matters

Opus 4.8 was the last Opus 4.x release and a bridge to the Mythos-class releases in June. It is still used as the fallback model inside Anthropic's safeguard stack.

## Your AI and this story

- GPT-6 Astra (training cutoff April 2026): 28 days after its cutoff
- Claude Opus 5.5 (training cutoff June 2026): in its training data
- Gemini 4 Hydrogen (training cutoff March 2026): 58 days after its cutoff
- Grok 4.7 (training cutoff May 2026): in its training data

## Sources

1. [Claude Code docs: model configuration (effort levels and ultracode)](https://code.claude.com/docs/en/model-config) (code.claude.com, docs)
2. [Introducing Claude Opus 4.8 (Anthropic)](https://www.anthropic.com/news/claude-opus-4-8) (anthropic.com, official)
3. [Pilot Shell: Ultracode in Claude Code, effort setting explained](https://pilot-shell.com/blog/ultracode) (pilot-shell.com, press)
4. [MacRumors: Opus 4.8 with gains in coding and honesty](https://www.macrumors.com/2026/05/28/anthropic-claude-opus-4-8/) (macrumors.com, press)
5. [Axios: Anthropic releases new model, Opus 4.8](https://www.axios.com/2026/05/28/anthropic-opus-release-mythos) (axios.com, press)
6. [9to5Mac: Anthropic upgrades Claude with Opus 4.8](https://9to5mac.com/2026/05/28/anthropic-upgrades-claude-with-new-opus-4-8-model-heres-whats-new/) (9to5mac.com, press)
7. [Simon Willison: Claude Opus 4.8 — a modest but tangible improvement](https://simonwillison.net/2026/May/28/claude-opus-4-8/) (simonwillison.net, discussion)

## Changes

- 2026-10-11: Added the ultracode setting
- 2026-09-29 (filed): Created

## Related

- 2026-06-09: [Anthropic releases Claude Fable 5 and Claude Mythos 5](https://postcutoff.com/e/2026-06-09-claude-fable-5-mythos-5/index.md)
- 2026-05-28: [Anthropic raises $65B Series H at $965B valuation, passing OpenAI](https://postcutoff.com/e/2026-05-28-anthropic-series-h-965b/index.md)
- 2026-04-16: [Anthropic releases Claude Opus 4.7, admits it trails the unreleased Mythos Preview](https://postcutoff.com/e/2026-04-16-claude-opus-4-7/index.md)
- People: [Simon Willison](https://postcutoff.com/person/simon-willison/)
- Archived: 10 videos, listed in https://postcutoff.com/e/2026-05-28-claude-opus-4-8/index.json