GPT-5.6 vs Earlier GPT-5 and GPT-4 Models: What Changed by 2026
The original GPT-5.1 comparison, preserved at the same URL and updated to explain today's model family, what each tier costs and how to route work across them.
The original address remains unchanged so existing backlinks and bookmarks continue to work.
The short answer: the original comparison is now history
When this URL was first published, GPT-5.1, GPT-5 and GPT-4 were useful comparison points. By August 2026, OpenAI’s model directory lists GPT-5.6 Sol, Terra and Luna as its current frontier family, with older GPT-5 releases retained as previous or deprecated options.
The durable buying question is no longer “which single GPT is best?” It is how to route work across capability, latency and cost tiers while keeping evaluation and review consistent.
How to think about the current family
- Sol: the frontier option for complex professional work.
- Terra: a balance of intelligence and operating cost.
- Luna: the cost-sensitive choice for routine and high-volume workloads.
Names will continue to change. Build evaluations around task difficulty, accepted output, latency and cost so a model can be replaced without redesigning the workflow.
What the tiers cost, and why that keeps changing
OpenAI published the GPT-5.6 family on 9 July 2026 with three list prices per million tokens: Sol at 5 dollars in and 30 out, Terra at 2.50 in and 15 out, and Luna at 1 in and 6 out. None of those figures survived the summer.
On 30 July 2026 OpenAI reduced Luna by 80 per cent and Terra by 20 per cent, and on 21 August 2026 it cut Sol by more than 20 per cent. Two rounds of cuts in six weeks tells you something more useful than any benchmark: per-token price is an active competitive lever, and a cost comparison built on launch-day numbers dates almost immediately. Check the vendor pricing page rather than trusting a figure in an article, including this one.
The tiers are also built to coexist rather than supersede one another. OpenAI describes them as durable capability tiers that advance on their own cadence, which is a direct invitation to route work by difficulty instead of sending everything to the most capable model available.
Routing work across tiers
- Send high-volume, low-ambiguity work such as classification, tagging and short-form generation to the cheapest tier.
- Keep everyday drafting, summarising and analysis on the balanced tier.
- Reserve the frontier tier for genuinely hard reasoning, long-context work and anything a person will act on without checking.
- Measure cost per accepted output rather than cost per call, since a cheap model that needs rewriting is not cheap.
- Re-test the routing whenever prices move, which in 2026 means roughly monthly.
Migration checklist
- Inventory model identifiers and deprecation dates.
- Run a fixed test set against the replacement model.
- Check tool calls, structured output and safety behaviour.
- Measure quality after human review—not benchmark scores alone.
- Roll out gradually with logs and a rollback path.
The current AI Writing & Research shortlist
Where this sits in the wider market: our current shortlist for AI Writing & Research, what each tool is best at and the main caution to check before committing.
| Tool | Best for | Current position | Important caution |
|---|---|---|---|
| ChatGPT Best all-rounder | General writing, analysis and multimodal work | GPT-5.6 combines strong reasoning with files, images, tools and broad workflow support. It is the safest starting point when one assistant must cover many jobs. | Teams should define data-handling rules and verify important claims. |
| Claude Long-form pick | Editorial work, complex documents and careful reasoning | Claude’s current Opus and Sonnet 5 family is built for sustained professional and agentic work, with a strong reputation for readable long-form output. | The highest-capability tiers can be unnecessary for routine copy. |
| Gemini Google ecosystem | Workspace users and multimodal source material | Gemini 3.7 Flash, documented in August 2026, is the current Flash release, connecting reasoning, multimodal inputs and Google’s productivity ecosystem. | Feature availability varies by Workspace plan and region. |
| Perplexity Research pick | Fast web research and cited discovery | Perplexity is useful when the first requirement is finding and comparing live web sources rather than drafting from memory. | A citation does not guarantee that the source supports every sentence; open the evidence. |
| Jasper Brand governance | Marketing teams with repeatable brand workflows | Jasper focuses on governed marketing content, brand context and campaign production rather than being a general-purpose chatbot. | Plans, limits and model availability change frequently; confirm the current vendor page before purchasing. |
| Copy.ai GTM workflows | Sales and marketing process automation | Copy.ai has evolved from a copy generator into a go-to-market workflow platform for repeatable content and sales operations. | Plans, limits and model availability change frequently; confirm the current vendor page before purchasing. |
| Writesonic AI visibility | SEO content and answer-engine monitoring | Writesonic combines assisted content production with tooling aimed at search and AI-answer visibility. | Plans, limits and model availability change frequently; confirm the current vendor page before purchasing. |
| Grammarly Editing layer | Everyday rewriting, tone and quality control | Grammarly works best as an editing and communication layer across existing applications rather than as the only writing system. | Plans, limits and model availability change frequently; confirm the current vendor page before purchasing. |
| Notion AI Knowledge workspace | Teams whose documents and projects already live in Notion | Notion AI is strongest when it can work inside an existing team knowledge base instead of requiring constant copying between tools. | Plans, limits and model availability change frequently; confirm the current vendor page before purchasing. |
| KoalaWriter SEO drafts | Structured long-form drafts and niche publishing | KoalaWriter remains a focused option for producing structured, search-aware drafts quickly. | Human research, original experience and fact-checking are still required before publishing. |
Related reading
Sources and verification notes
Primary product documentation checked for this update:
Product links
ChatGPT
Best for: General writing, analysis and multimodal work
GPT-5.6 combines strong reasoning with files, images, tools and broad workflow support. It is the safest starting point when one assistant must cover many jobs.
Watch: Teams should define data-handling rules and verify important claims.