NLP Lineage

22 September 2026 · Reasoning

Claude Opus 5.5

Claude Opus 5.5

Anthropic

Date
22 September 2026
What the date marks
Model release
Kind
Model
Organisation
Anthropic
Access
API only
Threads
In the guided tour
Chapter 14. Where the threads meet now
Learning phases
7. Agents

Too recent for its influence to be judged: no later milestone in the data descends from it yet. How levels are decided

Figures quoted here are reported by the organisation that built it, not independently verified.

Read the primary source (anthropic.com)

Full summary in progress. Until then, this page shows the milestone's record from the research data.

What it changed

Before it

Opus 5 had brought gated-tier capability closer to general availability.

The problem

The gap to the restricted Fable and Mythos tiers remained.

What it introduced

A release reported near Fable 5.1 capability at a substantially lower price.

Why it matters

The most recent entry in this timeline, at the edge of the verified record.

What modern models inherit

The present.

What came next

Beyond the verified record as of September 2026.

Before and after

The milestones it descends from, and the milestones that descend from it. Work developed alongside it is not counted. Weak links are left out unless you include them.

Before: where it came from

Claude Opus 5.5 has 54 documented ancestors across 10 chapters, reaching back to Recurrent networks in 1990. Showing its direct parents and the 18 turning points among them.

Claude Opus 5.5 has 54 documented ancestors across 10 chapters, reaching back to Recurrent networks in 1990. Showing all of them.

Claude Opus 5.5 has 58 recorded ancestors, including indirect ones, across 10 chapters, reaching back to Recurrent networks in 1990. Showing its direct parents and the 18 turning points among them.

Claude Opus 5.5 has 58 recorded ancestors, including indirect ones, across 10 chapters, reaching back to Recurrent networks in 1990. Showing all of them.

  1. 2026Claude Opus 5.5This milestone.
  2. 2026Claude Opus 5Claude Opus 5.5 built directly on thisChapter 14. Where the threads meet now
  3. 2026Claude Opus 4.8Claude Opus 5 succeeded thisChapter 14. Where the threads meet now
  4. 2026Claude Opus 4.7Claude Opus 4.8 built directly on thisChapter 14. Where the threads meet now
  5. 2026Claude Opus 4.6Claude Opus 4.7 built directly on thisChapter 14. Where the threads meet now
  6. 2025Claude Opus 4.5Claude Opus 4.6 built directly on thisChapter 13. Models that act
  7. 2025Claude Sonnet 4.5Claude Opus 4.5 built directly on thisChapter 13. Models that act
  8. 2025Claude 4Claude Sonnet 4.5 built directly on thisChapter 13. Models that act
  9. 2025Claude 3.7Claude 4 built directly on thisChapter 12. Thinking longer
  10. 2024o1 Turning pointClaude 3.7 was influenced by thisChapter 12. Thinking longer
  11. 2024Claude 3.5 SonnetClaude 3.7 built directly on thisChapter 14. Where the threads meet now
  12. 2024Claude 3Claude 4 succeeded thisChapter 14. Where the threads meet now
  13. 2023SWE-benchClaude Opus 4.5 was influenced by thisChapter 13. Models that act
  14. 2023GPT-4 Turning pointSWE-bench was influenced by thisChapter 7. The assistant goes public
  15. 2023ClaudeClaude 3 built directly on thisChapter 7. The assistant goes public
  16. 2022Constitutional AIClaude 3 built directly on thisChapter 6. Teaching models what people want
  17. 2022GPT-3.5 Turning pointGPT-4 succeeded thisChapter 7. The assistant goes public
  18. 2022HH-RLHFConstitutional AI built directly on this
    Claude was influenced by this    Chapter 6. Teaching models what people want
  19. 2022InstructGPT Turning pointGPT-4 built directly on thisChapter 6. Teaching models what people want
  20. 2022Chain of thought Turning pointo1 was influenced by this
    Constitutional AI was influenced by this    Chapter 12. Thinking longer
  21. 2021HHH assistantHH-RLHF built directly on thisChapter 6. Teaching models what people want
  22. 2021FLANInstructGPT was influenced by thisChapter 6. Teaching models what people want
  23. 2021Codex / HumanEvalSWE-bench built directly on thisChapter 13. Models that act
  24. 2020RLHF for summarisation Turning pointInstructGPT built directly on thisChapter 6. Teaching models what people want
  25. 2020GPT-3 Turning pointCodex / HumanEval built directly on thisChapter 5. Scale becomes a science
  26. 2020Scaling laws Turning pointGPT-4 built directly on thisChapter 5. Scale becomes a science
  27. 2019T5 Turning pointFLAN was influenced by thisChapter 4. Pretrain once, use everywhere
  28. 2019C4 Turning pointT5 was influenced by thisChapter 4. Pretrain once, use everywhere
  29. 2019RLHF for LMsRLHF for summarisation built directly on thisChapter 6. Teaching models what people want
  30. 2019Sparse Transformer Turning pointGPT-3 built directly on thisChapter 4. Pretrain once, use everywhere
  31. 2019GPT-2 Turning pointScaling laws was influenced by this
    GPT-3 built directly on this    Chapter 4. Pretrain once, use everywhere
  32. 2019WebTextGPT-2 was influenced by thisChapter 4. Pretrain once, use everywhere
  33. 2018BERT Turning pointT5 was influenced by thisChapter 4. Pretrain once, use everywhere
  34. 2018SentencePieceT5 built directly on thisChapter 4. Pretrain once, use everywhere
  35. 2018GPT-1GPT-2 built directly on thisChapter 4. Pretrain once, use everywhere
  36. 2018ELMoBERT was influenced by thisChapter 4. Pretrain once, use everywhere
  37. 2018ULMFiTBERT was influenced by thisChapter 4. Pretrain once, use everywhere
  38. 2017CoVeELMo was influenced by thisChapter 3. Attention, then only attention
  39. 2017Transformer Turning pointScaling laws built directly on thisChapter 3. Attention, then only attention
  40. 2017RLHF originRLHF for summarisation built directly on this
    Constitutional AI was influenced by this    Chapter 6. Teaching models what people want
  41. 2016Layer normTransformer built directly on this
    GPT-2 built directly on this    Chapter 3. Attention, then only attention
  42. 2015Residual connectionsTransformer was influenced by thisChapter 3. Attention, then only attention
  43. 2015LM pretraining Turning pointGPT-1 was influenced by thisChapter 2. Words become vectors
  44. 2015BPE tokenizationGPT-2 built directly on thisChapter 2. Words become vectors
  45. 2015Luong attentionTransformer was influenced by thisChapter 3. Attention, then only attention
  46. 2014AdamTransformer was influenced by thisChapter 2. Words become vectors
  47. 2014GloVeELMo built directly on thisChapter 2. Words become vectors
  48. 2014Seq2seq Turning pointTransformer built directly on thisChapter 2. Words become vectors
  49. 2014Attention Turning pointTransformer built directly on thisChapter 3. Attention, then only attention
  50. 2014GRU / encoder-decoderAttention built directly on thisChapter 2. Words become vectors
  51. 2013word2vecELMo was influenced by thisChapter 2. Words become vectors
  52. 2011NLP from scratchELMo was influenced by thisChapter 1. Language as probability
  53. 2003Neural LMNLP from scratch was influenced by this
    word2vec was influenced by this    Chapter 1. Language as probability
  54. 1997LSTM Turning pointSeq2seq built directly on thisChapter 1. Language as probability
  55. 1990Recurrent networksLSTM was influenced by thisChapter 1. Language as probability
  1. 2026Claude Opus 5.5This milestone.
  2. 2026Claude Opus 5Claude Opus 5.5 built directly on thisChapter 14. Where the threads meet now
  3. 2026Claude Opus 4.8Claude Opus 5 succeeded thisChapter 14. Where the threads meet now
  4. 2026Claude Opus 4.7Claude Opus 4.8 built directly on thisChapter 14. Where the threads meet now
  5. 2026Claude Opus 4.6Claude Opus 4.7 built directly on thisChapter 14. Where the threads meet now
  6. 2025Claude Opus 4.5Claude Opus 4.6 built directly on thisChapter 13. Models that act
  7. 2025Claude Sonnet 4.5Claude Opus 4.5 built directly on thisChapter 13. Models that act
  8. 2025Claude 4Claude Sonnet 4.5 built directly on thisChapter 13. Models that act
  9. 2025Claude 3.7Claude 4 built directly on thisChapter 12. Thinking longer
  10. 2024o1 Turning pointClaude 3.7 was influenced by thisChapter 12. Thinking longer
  11. 2024Claude 3.5 SonnetClaude 3.7 built directly on thisChapter 14. Where the threads meet now
  12. 2024Claude 3Claude 4 succeeded thisChapter 14. Where the threads meet now
  13. 2023SWE-benchClaude Opus 4.5 was influenced by thisChapter 13. Models that act
  14. 2023Process supervisiono1 was influenced by this (indirect influence)Chapter 12. Thinking longer
  15. 2023GPT-4 Turning pointSWE-bench was influenced by thisChapter 7. The assistant goes public
  16. 2023ClaudeClaude 3 built directly on thisChapter 7. The assistant goes public
  17. 2022Constitutional AIClaude 3 built directly on thisChapter 6. Teaching models what people want
  18. 2022GPT-3.5 Turning pointGPT-4 succeeded thisChapter 7. The assistant goes public
  19. 2022HH-RLHFConstitutional AI built directly on this
    Claude was influenced by this    Chapter 6. Teaching models what people want
  20. 2022STaRo1 was influenced by this (indirect influence)Chapter 12. Thinking longer
  21. 2022InstructGPT Turning pointGPT-4 built directly on thisChapter 6. Teaching models what people want
  22. 2022Chain of thought Turning pointo1 was influenced by this
    Constitutional AI was influenced by this    Chapter 12. Thinking longer
  23. 2021HHH assistantHH-RLHF built directly on thisChapter 6. Teaching models what people want
  24. 2021FLANInstructGPT was influenced by thisChapter 6. Teaching models what people want
  25. 2021Codex / HumanEvalSWE-bench built directly on thisChapter 13. Models that act
  26. 2020RLHF for summarisation Turning pointInstructGPT built directly on thisChapter 6. Teaching models what people want
  27. 2020GPT-3 Turning pointCodex / HumanEval built directly on thisChapter 5. Scale becomes a science
  28. 2020Scaling laws Turning pointGPT-4 built directly on thisChapter 5. Scale becomes a science
  29. 2019T5 Turning pointFLAN was influenced by thisChapter 4. Pretrain once, use everywhere
  30. 2019C4 Turning pointT5 was influenced by thisChapter 4. Pretrain once, use everywhere
  31. 2019RLHF for LMsRLHF for summarisation built directly on thisChapter 6. Teaching models what people want
  32. 2019Sparse Transformer Turning pointGPT-3 built directly on thisChapter 4. Pretrain once, use everywhere
  33. 2019GPT-2 Turning pointScaling laws was influenced by this
    GPT-3 built directly on this    Chapter 4. Pretrain once, use everywhere
  34. 2019WebTextGPT-2 was influenced by thisChapter 4. Pretrain once, use everywhere
  35. 2019Transformer-XLSparse Transformer was influenced by this (indirect influence)Chapter 4. Pretrain once, use everywhere
  36. 2018BERT Turning pointT5 was influenced by thisChapter 4. Pretrain once, use everywhere
  37. 2018SentencePieceT5 built directly on thisChapter 4. Pretrain once, use everywhere
  38. 2018GPT-1GPT-2 built directly on thisChapter 4. Pretrain once, use everywhere
  39. 2018ELMoGPT-1 was influenced by this (indirect influence)Chapter 4. Pretrain once, use everywhere
  40. 2018ULMFiTGPT-1 was influenced by this (indirect influence)Chapter 4. Pretrain once, use everywhere
  41. 2017CoVeELMo was influenced by thisChapter 3. Attention, then only attention
  42. 2017Transformer Turning pointScaling laws built directly on thisChapter 3. Attention, then only attention
  43. 2017RLHF originRLHF for summarisation built directly on this
    o1 was influenced by this (indirect influence)
    Constitutional AI was influenced by this    Chapter 6. Teaching models what people want
  44. 2017ConvS2STransformer was influenced by this (indirect influence)Chapter 3. Attention, then only attention
  45. 2016Layer normTransformer built directly on this
    GPT-2 built directly on this    Chapter 3. Attention, then only attention
  46. 2015Residual connectionsTransformer was influenced by thisChapter 3. Attention, then only attention
  47. 2015LM pretraining Turning pointGPT-1 was influenced by thisChapter 2. Words become vectors
  48. 2015BPE tokenizationGPT-2 built directly on thisChapter 2. Words become vectors
  49. 2015Luong attentionTransformer was influenced by thisChapter 3. Attention, then only attention
  50. 2014AdamTransformer was influenced by thisChapter 2. Words become vectors
  51. 2014GloVeELMo built directly on thisChapter 2. Words become vectors
  52. 2014Seq2seq Turning pointTransformer built directly on thisChapter 2. Words become vectors
  53. 2014Attention Turning pointTransformer built directly on thisChapter 3. Attention, then only attention
  54. 2014GRU / encoder-decoderAttention built directly on thisChapter 2. Words become vectors
  55. 2013word2vecELMo was influenced by thisChapter 2. Words become vectors
  56. 2011NLP from scratchELMo was influenced by thisChapter 1. Language as probability
  57. 2003Neural LMNLP from scratch was influenced by this
    word2vec was influenced by this    Chapter 1. Language as probability
  58. 1997LSTM Turning pointSeq2seq built directly on thisChapter 1. Language as probability
  59. 1990Recurrent networksLSTM was influenced by thisChapter 1. Language as probability

After: what it led to

No documented descendants are recorded for Claude Opus 5.5 without weak links.

No documented descendants are recorded for Claude Opus 5.5 without weak links.

No recorded descendants are recorded for Claude Opus 5.5.

No recorded descendants are recorded for Claude Opus 5.5.

Direct links and their sources

Where it came from

Built directly on

What it led to

None recorded in the sources used.