NLP Lineage

23 April 2026 · Reasoning

GPT-5.5

GPT-5.5

OpenAI

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

A milestone: 1 later milestone descends directly from it, and its descendants reach 1 of the 10 threads. How levels are decided

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

Read the primary source (openai.com)

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

What it changed

Before it

Terminal-based agent benchmarks were the new contested ground.

The problem

Long tool-using sessions expose reliability problems that short benchmarks miss.

What it introduced

A release reported at 82.7% on Terminal-Bench 2.0.

Why it matters

Marks the shift of competition from code-patch benchmarks to full terminal sessions.

What modern models inherit

Terminal and computer-use benchmarks as the frontier measure.

What came next

The GPT-5.6 Sol family in July.

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

GPT-5.5 has 48 documented ancestors across 11 chapters, reaching back to Recurrent networks in 1990. Showing its direct parents and the 18 turning points among them.

GPT-5.5 has 48 documented ancestors across 11 chapters, reaching back to Recurrent networks in 1990. Showing all of them.

GPT-5.5 has 68 recorded ancestors, including indirect ones, across 11 chapters, reaching back to Recurrent networks in 1990. Showing its direct parents and the 18 turning points among them.

GPT-5.5 has 68 recorded ancestors, including indirect ones, across 11 chapters, reaching back to Recurrent networks in 1990. Showing all of them.

  1. 2026GPT-5.5This milestone.
  2. 2026GPT-5.4GPT-5.5 built directly on thisChapter 14. Where the threads meet now
  3. 2026GPT-5.3-CodexGPT-5.4 built directly on thisChapter 13. Models that act
  4. 2025GPT-5.2GPT-5.3-Codex built directly on thisChapter 14. Where the threads meet now
  5. 2025GPT-5.1GPT-5.2 built directly on thisChapter 14. Where the threads meet now
  6. 2025GPT-5GPT-5.1 built directly on thisChapter 14. Where the threads meet now
  7. 2025o3 releasedGPT-5 built directly on thisChapter 12. Thinking longer
  8. 2024o3 announcedo3 released succeeded thisChapter 12. Thinking longer
  9. 2024o1 Turning pointo3 released built directly on thisChapter 12. Thinking longer
  10. 2024GPT-4oGPT-5 succeeded thisChapter 11. Seeing and hearing
  11. 2023GPT-4VGPT-4o built directly on thisChapter 11. Seeing and hearing
  12. 2023Function callingo3 released was influenced by thisChapter 13. Models that act
  13. 2023GPT-4 Turning pointGPT-4o built directly on thisChapter 7. The assistant goes public
  14. 2022GPT-3.5 Turning pointGPT-4 succeeded thisChapter 7. The assistant goes public
  15. 2022InstructGPT Turning pointGPT-4 built directly on thisChapter 6. Teaching models what people want
  16. 2022Chain of thought Turning pointo1 was influenced by thisChapter 12. Thinking longer
  17. 2021FLANInstructGPT was influenced by thisChapter 6. Teaching models what people want
  18. 2020RLHF for summarisation Turning pointInstructGPT built directly on thisChapter 6. Teaching models what people want
  19. 2020GPT-3 Turning pointChain of thought was influenced by this
    InstructGPT built directly on this
    GPT-3.5 built directly on this    Chapter 5. Scale becomes a science
  20. 2020Scaling laws Turning pointGPT-4 built directly on thisChapter 5. Scale becomes a science
  21. 2019T5 Turning pointFLAN was influenced by thisChapter 4. Pretrain once, use everywhere
  22. 2019C4 Turning pointT5 was influenced by thisChapter 4. Pretrain once, use everywhere
  23. 2019RLHF for LMsRLHF for summarisation built directly on thisChapter 6. Teaching models what people want
  24. 2019Sparse Transformer Turning pointGPT-3 built directly on thisChapter 4. Pretrain once, use everywhere
  25. 2019GPT-2 Turning pointScaling laws was influenced by thisChapter 4. Pretrain once, use everywhere
  26. 2019WebTextGPT-2 was influenced by thisChapter 4. Pretrain once, use everywhere
  27. 2018BERT Turning pointT5 was influenced by thisChapter 4. Pretrain once, use everywhere
  28. 2018SentencePieceT5 built directly on thisChapter 4. Pretrain once, use everywhere
  29. 2018GPT-1GPT-2 built directly on thisChapter 4. Pretrain once, use everywhere
  30. 2018ELMoBERT was influenced by thisChapter 4. Pretrain once, use everywhere
  31. 2018ULMFiTBERT was influenced by thisChapter 4. Pretrain once, use everywhere
  32. 2017CoVeELMo was influenced by thisChapter 3. Attention, then only attention
  33. 2017Transformer Turning pointScaling laws built directly on thisChapter 3. Attention, then only attention
  34. 2017RLHF originRLHF for summarisation built directly on thisChapter 6. Teaching models what people want
  35. 2016Layer normTransformer built directly on this
    GPT-2 built directly on this    Chapter 3. Attention, then only attention
  36. 2015Residual connectionsTransformer was influenced by thisChapter 3. Attention, then only attention
  37. 2015LM pretraining Turning pointGPT-1 was influenced by thisChapter 2. Words become vectors
  38. 2015BPE tokenizationGPT-2 built directly on thisChapter 2. Words become vectors
  39. 2015Luong attentionTransformer was influenced by thisChapter 3. Attention, then only attention
  40. 2014AdamTransformer was influenced by thisChapter 2. Words become vectors
  41. 2014GloVeELMo built directly on thisChapter 2. Words become vectors
  42. 2014Seq2seq Turning pointTransformer built directly on thisChapter 2. Words become vectors
  43. 2014Attention Turning pointTransformer built directly on thisChapter 3. Attention, then only attention
  44. 2014GRU / encoder-decoderAttention built directly on thisChapter 2. Words become vectors
  45. 2013word2vecELMo was influenced by thisChapter 2. Words become vectors
  46. 2011NLP from scratchELMo was influenced by thisChapter 1. Language as probability
  47. 2003Neural LMNLP from scratch was influenced by this
    word2vec was influenced by this    Chapter 1. Language as probability
  48. 1997LSTM Turning pointSeq2seq built directly on thisChapter 1. Language as probability
  49. 1990Recurrent networksLSTM was influenced by thisChapter 1. Language as probability
  1. 2026GPT-5.5This milestone.
  2. 2026GPT-5.4GPT-5.5 built directly on thisChapter 14. Where the threads meet now
  3. 2026GPT-5.3-CodexGPT-5.4 built directly on thisChapter 13. Models that act
  4. 2025GPT-5.2GPT-5.3-Codex built directly on thisChapter 14. Where the threads meet now
  5. 2025GPT-5.1GPT-5.2 built directly on thisChapter 14. Where the threads meet now
  6. 2025GPT-5GPT-5.1 built directly on thisChapter 14. Where the threads meet now
  7. 2025o3 releasedGPT-5 built directly on thisChapter 12. Thinking longer
  8. 2024o3 announcedo3 released succeeded thisChapter 12. Thinking longer
  9. 2024Computer useGPT-5.3-Codex was influenced by this (indirect influence)Chapter 13. Models that act
  10. 2024o1 Turning pointo3 released built directly on thisChapter 12. Thinking longer
  11. 2024Test-time computeo3 announced was influenced by this (indirect influence)Chapter 12. Thinking longer
  12. 2024Claude 3.5 SonnetComputer use built directly on thisChapter 14. Where the threads meet now
  13. 2024GPT-4oGPT-5 succeeded thisChapter 11. Seeing and hearing
  14. 2024Claude 3Claude 3.5 Sonnet built directly on thisChapter 14. Where the threads meet now
  15. 2023GPT-4VComputer use was influenced by thisChapter 11. Seeing and hearing
  16. 2023Function callingComputer use was influenced by this (indirect influence)Chapter 13. Models that act
  17. 2023Process supervisiono1 was influenced by this (indirect influence)Chapter 12. Thinking longer
  18. 2023Tree of thoughtsTest-time compute was influenced by this (indirect influence)Chapter 12. Thinking longer
  19. 2023GPT-4 Turning pointGPT-4V built directly on thisChapter 7. The assistant goes public
  20. 2023ClaudeClaude 3 built directly on thisChapter 7. The assistant goes public
  21. 2023ToolformerFunction calling was influenced by this (indirect influence)Chapter 13. Models that act
  22. 2022Constitutional AIClaude 3 built directly on thisChapter 6. Teaching models what people want
  23. 2022GPT-3.5 Turning pointGPT-4 succeeded thisChapter 7. The assistant goes public
  24. 2022ReActFunction calling was influenced by this (indirect influence)Chapter 13. Models that act
  25. 2022WhisperGPT-4o was influenced by this (indirect influence)Chapter 11. Seeing and hearing
  26. 2022HH-RLHFConstitutional AI built directly on this
    Claude was influenced by this    Chapter 6. Teaching models what people want
  27. 2022STaRo1 was influenced by this (indirect influence)Chapter 12. Thinking longer
  28. 2022Self-consistencyTest-time compute built directly on thisChapter 12. Thinking longer
  29. 2022InstructGPT Turning pointGPT-4 built directly on thisChapter 6. Teaching models what people want
  30. 2022Chain of thought Turning pointReAct built directly on thisChapter 12. Thinking longer
  31. 2021WebGPTReAct was influenced by this
    Toolformer was influenced by this    Chapter 13. Models that act
  32. 2021HHH assistantHH-RLHF built directly on thisChapter 6. Teaching models what people want
  33. 2021FLANInstructGPT was influenced by thisChapter 6. Teaching models what people want
  34. 2021CLIPGPT-4V was influenced by this (indirect influence)Chapter 11. Seeing and hearing
  35. 2020Vision TransformerCLIP built directly on thisChapter 11. Seeing and hearing
  36. 2020RLHF for summarisation Turning pointInstructGPT built directly on this
    WebGPT built directly on this    Chapter 6. Teaching models what people want
  37. 2020GPT-3 Turning pointToolformer built directly on thisChapter 5. Scale becomes a science
  38. 2020Scaling laws Turning pointGPT-4 built directly on thisChapter 5. Scale becomes a science
  39. 2019T5 Turning pointFLAN was influenced by thisChapter 4. Pretrain once, use everywhere
  40. 2019C4 Turning pointT5 was influenced by thisChapter 4. Pretrain once, use everywhere
  41. 2019RLHF for LMsRLHF for summarisation built directly on thisChapter 6. Teaching models what people want
  42. 2019Sparse Transformer Turning pointGPT-3 built directly on thisChapter 4. Pretrain once, use everywhere
  43. 2019GPT-2 Turning pointCLIP built directly on thisChapter 4. Pretrain once, use everywhere
  44. 2019WebTextGPT-2 was influenced by thisChapter 4. Pretrain once, use everywhere
  45. 2019Transformer-XLSparse Transformer was influenced by this (indirect influence)Chapter 4. Pretrain once, use everywhere
  46. 2018BERT Turning pointVision Transformer was influenced by thisChapter 4. Pretrain once, use everywhere
  47. 2018SentencePieceT5 built directly on thisChapter 4. Pretrain once, use everywhere
  48. 2018GPT-1GPT-2 built directly on thisChapter 4. Pretrain once, use everywhere
  49. 2018ELMoBERT was influenced by this
    GPT-1 was influenced by this (indirect influence)    Chapter 4. Pretrain once, use everywhere
  50. 2018ULMFiTBERT was influenced by this
    GPT-1 was influenced by this (indirect influence)    Chapter 4. Pretrain once, use everywhere
  51. 2017CoVeELMo was influenced by thisChapter 3. Attention, then only attention
  52. 2017RLHF originConstitutional AI was influenced by thisChapter 6. Teaching models what people want
  53. 2017Transformer Turning pointGPT-2 built directly on this
    Scaling laws built directly on this
    Vision Transformer built directly on this    Chapter 3. Attention, then only attention
  54. 2017ConvS2STransformer was influenced by this (indirect influence)Chapter 3. Attention, then only attention
  55. 2016Layer normGPT-2 built directly on thisChapter 3. Attention, then only attention
  56. 2015Residual connectionsTransformer was influenced by thisChapter 3. Attention, then only attention
  57. 2015LM pretraining Turning pointBERT was influenced by this
    GPT-1 was influenced by this    Chapter 2. Words become vectors
  58. 2015BPE tokenizationGPT-2 built directly on thisChapter 2. Words become vectors
  59. 2015Luong attentionTransformer was influenced by thisChapter 3. Attention, then only attention
  60. 2014AdamTransformer was influenced by thisChapter 2. Words become vectors
  61. 2014GloVeELMo built directly on thisChapter 2. Words become vectors
  62. 2014Seq2seq Turning pointTransformer built directly on thisChapter 2. Words become vectors
  63. 2014Attention Turning pointTransformer built directly on thisChapter 3. Attention, then only attention
  64. 2014GRU / encoder-decoderAttention built directly on thisChapter 2. Words become vectors
  65. 2013word2vecELMo was influenced by thisChapter 2. Words become vectors
  66. 2011NLP from scratchELMo was influenced by thisChapter 1. Language as probability
  67. 2003Neural LMNLP from scratch was influenced by this
    word2vec was influenced by this    Chapter 1. Language as probability
  68. 1997LSTM Turning pointSeq2seq built directly on this
    ELMo built directly on this    Chapter 1. Language as probability
  69. 1990Recurrent networksLSTM was influenced by thisChapter 1. Language as probability

After: what it led to

GPT-5.5 has 1 documented descendants across 1 chapter, reaching forward to GPT-5.6 Sol in 2026. Showing all of them.

GPT-5.5 has 1 documented descendants across 1 chapter, reaching forward to GPT-5.6 Sol in 2026. Showing all of them.

GPT-5.5 has 1 recorded descendants, including indirect ones, across 1 chapter, reaching forward to GPT-5.6 Sol in 2026. Showing all of them.

GPT-5.5 has 1 recorded descendants, including indirect ones, across 1 chapter, reaching forward to GPT-5.6 Sol in 2026. Showing all of them.

  1. 2026GPT-5.5This milestone.
  2. 2026GPT-5.6 Solbuilt directly on GPT-5.5Chapter 14. Where the threads meet now
  1. 2026GPT-5.5This milestone.
  2. 2026GPT-5.6 Solbuilt directly on GPT-5.5Chapter 14. Where the threads meet now

Direct links and their sources

Where it came from

Built directly on

What it led to

Built on directly by