Steve Rabin, the editor of book Game AI Pro 3 have just released the title completely for free on their website http://www.gameaipro.com/. Due to details with their publisher the book rights remain those of CRC Press and cannot be redistributed or hosted anywhere else. Additionally the book is split into multiple chapters, each 
available as individual PDF chapters, although merging multiple PDFs is a relatively simple task if preferred.
Links to each chapter:
Section 1: General Wisdom
1. The Illusion of Intelligence, Steve Rabin
2. Creating the Past, Present, and Future with Random Walks, John Manslow demo code
3. Logging Visualization in FINAL FANTASY XV, Matthew W. Johnson, Fabien Gravot, Shintaro Minamino, Ingimar Hólm Guðmundsson, Hendrik Skubch, and Youichiro Miyake
4. What You See Is Not What You Get: Player Perception of AI Opponents, Baylor Wetzel and Kyle Anderson
5. Six Factory System Tricks for Extensibility and Library Reuse, Kevin Dill
6. Debugging AI with Instant In-Game Scrubbing, David Young
7. But, It Worked on My Machine! How to Build Robust AI for Your Game, Sergio Ocio BarrialesSection 2: Architecture
8. Modular AI, Kevin Dill and Christopher Dragert
9. Overcoming Pitfalls in Behavior Tree Design, Anthony Francis
10. From Behavior to Animation: A Reactive AI Architecture for Networked First-Person Shooter Games, Sumeet Jakatdar
11. A Character Decision-Making System for FINAL FANTASY XV by Combining Behavior Trees and State Machines, Youichiro Miyake, Youji Shirakami, Kazuya Shimokawa, Kousuke Namiki, Tomoki Komatsu, Joudan Tatsuhiro, Prasert Prasertvithyakarn, and Takanori Yokoyama
12. A Reusable, Light-Weight Finite-State Machine, David “Rez” Graham
13. Choosing Effective Utility-Based Considerations, Mike Lewis
14. Combining Scripted Behavior with Game Tree Search for Stronger, More Robust Game AI, Nicolas A. Barriga, Marius Stanescu, and Michael BuroSection 3: Movement and Pathfinding
15. Steering against Complex Vehicles in Assassin’s Creed Syndicate, Eric Martel
16. Predictive Animation Control Using Simulations and Fitted Models, Ingimar Hólm Guðmundsson, Hendrik Skubch, Fabien Gravot, and Youichiro Miyake
17. Fast Cars, Big City: The AI of Driver San Francisco, Chris Jenner and Sergio Ocio Barriales
18. A Unified Theory of Locomotion, Graham Pentheny
19. RVO and ORCA: How They Really Work, Ben Sunshine-Hill
20. Optimization for Smooth Paths, Mark Langerak demo code
21. 3D Flight Navigation Using Sparse Voxel Octrees, Daniel Brewer
22. Faster A* with Goal Bounding, Steve Rabin and Nathan R. Sturtevant
23. Faster Dijkstra Search on Uniform Cost Grids, Steve Rabin and Nathan R. SturtevantSection 4: Tactics and Strategy
24. Being Where It Counts: Telling Paragon Bots Where to Go, Mieszko Zieliński
25. Combat Outcome Prediction for Real-Time Strategy Games, Marius Stanescu, Nicolas A. Barriga, and Michael Buro
26. Guide to Effective Auto-Generated Spatial Queries, Eric Johnson
27. The Role of Time in Spatio-Temporal Reasoning: Three Examples from Tower Defense, Baylor Wetzel and Kyle Anderson
28. Pitfalls and Solutions When Using Monte-Carlo Tree Search for Strategy and Tactical Games, Gijs-Jan Roelofs
29. Petri Nets and AI Arbitration, Sergio Ocio Barriales
30. Hierarchical Portfolio Search in Prismata, David Churchill and Michael BuroSection 6: Character Behavior
31. Behavior Decision System: Dragon Age Inquisition’s Utility Scoring Architecture, Sebastian Hanlon and Cody Watts
32. Paragon Bots: A Bag of Tricks, Mieszko Zieliński
33. Using Your Combat AI Accuracy to Balance Difficulty, Sergio Ocio Barriales
34. 1000 NPCs at 60 FPS, Robert Zubek
35. Ambient Interactions: Improving Believability by Leveraging Rule-Based AI, Hendrik Skubch
36. Stochastic Grammars: Not Just for Words!, Mike Lewis demo code
37. Simulating Character Knowledge Phenomena in Talk of the Town, James Ryan and Michael MateasSection 7: Odds and Ends
38. Procedural Level and Story Generation Using Tag-Based Content Selection, Jurie Horneman
39. Recommendation Systems in Games, Ben G. Weber
40. Vintage Random Number Generators, Éric Jacopin demo code
41. Leveraging Plausibility Orderings to Achieve Extremely Efficient Data Compression, Jeff Rollason
42. Building Custom Static Checkers Using Declarative Programming, Ian Horswill, Robert Zubek, and Matthew Viglione
On the same page you can also download first and second editions of the Game AI book series. Awesome contribution from the editor and all the various others and such a huge wealth of knowledge being shared.
Source : http://www.gamefromscratch.com/post/2020/01/30/Game-AI-Pro-3-Now-Available-Free.aspx