AC Model is the 3DCG model used for “39’s Giving Day” concert in 2010  . It is also known as “Old AC” “39’s giving Model” “Ake Miku (Arcade Miku)”. This model is developed by SEGA AM2 division (Second Division of developing Arcade games), and also used by Project DIVA Arcade and Dreamy Theater Series.
This model is mostly same as Hatsune Miku : Project DIVA Arcade (aka DIVA Arcade).
The model is based on PSP model rendered throughout VirtuaFighter 5’s game engine  , which is created for “MikuFES’09 (Summer)” in Aug 2009. PSP model on VF5 engine had similarity with AC model, with physics engine for hair and self shadow features  .
In same years September 17th, SEGA post the video which VF5 based Miku dances the song Melt . However, at this time SEGA have not revealed the corporation by AM2. Few weeks later, SEGA posted another video revealing that “MikuFES’09 (Summer)” used two different method, and publicly announcing the VF5 engine’s usage  .
After October, SEGA stopped using VF5 based Miku. By this time, SEGA fork the project out of VF5  , becoming “Project DIVA Arcade”.
The model it self was revealed by November for DIVA Arcade’s song public offering campaign. However, only picture were available, and video did not exist.
In December 17th 2009, SEGA finally released video of moving AC model, which was created for advertise video of “39’s giving day” concert  . By this time, it become public that both 39’s giving day and DIVA Arcade are using same, new high quality, model. Also about a week later from this advertisement video’s reveal, SEGA announced DIVA Arcade’s “Location test” with video  .
In AOU 2010, held in Makuhari Messe at February 19 and 20th 2010, SEGA held demo play booth, with first AC model based mini concert  . The song used for this concert was StargazeR, and melt  . Usually, majority claims “39’s giving day” as first concert of AC model; however, actual first concert for AC model was 2 weeks before 39’s giving day, at Makuhari Messe.
And the model was used for “39’s giving day” concert in March 9th 2010. 3 month later, in June, SEGA finally released Project DIVA Arcade, and Dreamy theater.
In 2012, AC model reached its “Finale” with Final 39’s giving concert. Although model is still used now, its limited to few songs.
Also, FT model, successor to AC model, do exists and some songs are re-rendered with this newer model.
By the time this model was created, console game’s DIVA was PSP game. While PSP has only half of performance of PS2  , RINGEDGE, SEGA’s arcade board using Pentium with Windows, was over performing. Thus, AC model is more high quality, with more polygons and better shader, and constant 60fps.
Because of its origins, it have similarities with PSP model handled by AM2. For example, hair smoothness is same since initial PSP model on VF5, throughout final version of AC model. Also, unlike other models, many technical information are publicized by SEGA. One major example is” pjd technical club” (pjd技術部), which have 4 articles relating to AC model  , and technical information of DIVA Arcade.
Also, arcade board information tends to be more public from earlier stage, thus being most easiest model to gain information.
Because AC model, and Project DIVA Arcade started from “Running Miku on Virtua Fighter 5”, it have many similarities with VF5. Like VF5, it runs on OpenGL  , and both port version uses same engine and OpenGL compatible library  . Also, Project DIVA Arcade actually runs on LINDBERGH  , predecessor board with VF5 runs, with limited functionality, which leads up that AC model have similarities with VF5.
Of course the upgrade from LINDBERGH series introduced like better quality self shadow  , and adjustments with skin and eyes  . AC model and DIVA Arcade is not product that is only build on VF5 technology, which is obsolete by 2010.
Concert information is also widely available to public. For example, computer used to render Final 39’s giving concert had GeForce GTX 570, with 3240*1080 resolution  .This is only concert that rendering PC’s specification are public.
(R3 mini concert in Magical Mirai 2017 have specs public, but since this is “Free concert” with demo, its not “Regular concert” like Magical Mirai or MIKU EXPO. )
Also, with Kagamine and Megurine series was introduced from initial launch  , and MEIKO is used for Final 39’s giving concert  .
This is first model that introduced CV series into concert. However, KAITO was not used at all, as AC model. First debut of KAITO is MikuPa 2012 Tokyo, which is concert held day before Final 39’s giving day.
Concert that uses AC model
AC model is oldest 3DCG model used currently, in 2018.
All songs presented in MIKUNOPOLIS  , and Final 39’s giving day  is AC model. 39’s giving in 2010 have few songs that are presented by PSP model, but it mostly uses AC model  . These concert are usually called “39’s giving series”, and being AC model exclusive concert.
After 2012, the model was never used until 2015, at MIKU EXPO 2015 Shanghai, and MIKU EXPO held later. Magical Mirai sticked with F model (With one FT model song), but started to use AC model from 2017.
Evidence (Using something similar to MLA 8)
 ファミ通.com. “ミクの日感謝祭 39’s Giving Dayに行ってきたぞ！” ファミ通.com, 15 Mar. 2010, www.famitsu.com/blog/arcadia/2010/03/_39s_giving_day.html.
 SEGA feat. HATSUNE MIKU ちゃんねる. “【初音ミク】本気でミクFESに参加してみた【Project DIVA】.” ニコニコ動画, 15 Oct. 2009, www.nicovideo.jp/watch/1255673703.
 SEGA feat. HATSUNE MIKU ちゃんねる. “初音ミク-ProjectDIVA-（新）始動！” ニコニコ動画, 17 Sept. 2009, www.nicovideo.jp/watch/1253185516.
 SEGA. “pjd技術部：第三回「初音ミク Project DIVA Arcadeとミクの日感謝祭とVirtua Fighter 5」” SEGA.jp, 16 Apr. 2012, http://info.miku.sega.jp/565.
 SEGA feat. HATSUNE MIKU ちゃんねる. “【初音ミク】ミクの日感謝祭CM「でぃばでぃば～」篇【Project DIVA】.” ニコニコ動画, 17 Dec. 2009, http://www.nicovideo.jp/watch/1260871203.
 SEGA feat. HATSUNE MIKU ちゃんねる. “【Project DIVA Arcade】ロケテスト情報！.” ニコニコ動画, 24 Dec. 2009, http://www.nicovideo.jp/watch/1261636716.
 ファミ通.com . “AOU 2010開幕――『メタルギア アーケード』、『Project DIVA Arcade』に人気が集中.” ファミ通.com, 19 Feb. 2010, https://www.famitsu.com/game/news/1232269_1124.html
 ジーパラドットコム. “【AOU2010】試遊レポ『Project DIVA Arcade』美しいミク、良音質、大混雑！.” ジーパラドットコム, Gpara.com, 19 Feb. 2010, www.gpara.com/article/cms_show.php?c_id=18918.
 後藤弘茂. “PlayStation 2に迫るPSPのグラフィックスコア” 後藤弘茂のWeekly海外ニュース, 4 Aug. 2003, pc.watch.impress.co.jp/docs/2003/0804/kaigai009.htm.
 2号 (大崎 誠) “検索結果: Pjd技術部.” 週刊ディーヴァ・ステーション | セガ, info.miku.sega.jp/?s=pjd技術部.
 小西利明. “セガ，次世代アーケードゲーム基板「Nu」を発表。採用タイトル第1弾は「初音ミク Project DIVA Arcade Future Tone」に” 4Gamer.net, 4 Sept. 2013, 4gamer.net/games/999/G999902/20130904019/.
 SEGA “セガ，業務用ゲーム汎用基板「RINGEDGE」「RINGWIDE」を開発” 4Gamer.net, 20 Feb. 2009, 4gamer.net/games/000/G000000/20090220004/.
 ファミ通.com . “『初音ミク』の10年と、『ディーヴァ』シリーズの歩みを振り返る。クリプトン佐々木氏＆セガ大崎氏インタビュー.” ファミ通.com, 11 Dec. 2017, www.famitsu.com/news/201712/11146884.html.
 さくま＠ミクさん担当 . “『最後のミクの日感謝祭』速報 ビッグサプライズもあった!?” 週刊アスキー, 9 Mar. 2012, weekly.ascii.jp/elem/000/000/079/79425/.
 さくま＠ミクさん担当 . “ミクパ2012速報！ ミクさんがマジで天使になった日” 週刊アスキー, 8 Mar. 2012, weekly.ascii.jp/elem/000/000/079/79322/
 広田稔. “5000人が燃えた！ 『MIKUNOPOLIS in LOS ANGELES』ライブ徹底レポート”週刊アスキー, 4 Jul 2011, weekly.ascii.jp/elem/000/000/048/48120/
 @makoosa (Makoto Osaki). “《一応DIVAアーケード的な答え合わせ》★FTミクさん：初音ミクの消失/愛言葉/恋は戦争/積乱雲グラフィティ ★旧AC系：WEDH/magnet/Change me 上記以外はFモデル/ミクパモデルです。” Twitter, 10 Apr. 2016, 9:44 p.m. (JST) https://twitter.com/makoosa/status/719144042605318146